Why $/GB alone tells you almost nothing
A headline price per gigabyte only means something once you know what's loading through that gigabyte, because a GB spent on JSON API calls and a GB spent on full rendered pages with images and JS are not the same purchase. This is the exact confusion running through a lot of proxy shopping threads: someone posts a rate, someone else asks "compared to what," and nobody answers because nobody defined the target. One practitioner laid this out clearly in a widely discussed r/proxies thread on proxy quality: "proxy quality is not an absolute property of an IP... why certain proxies work on one target but fail badly on another" is the whole point. The same logic applies to bandwidth. A $/GB number isn't a quality score. It isn't a cost score either. It's a fragment of one, and treating it as the whole picture is how people end up overpaying for what looks like the cheaper plan.
Residential (rotating) proxies are billed per GB because the provider genuinely doesn't know in advance how much data your traffic will move; you're renting access to a pool and paying for what you pull through it. ISP (static) proxies are billed per IP, flat, because you're renting a fixed set of dedicated addresses, not metered throughput. On BirdProxies specifically, that split is literal: ISP plans start at €1.40 per IP for 25 IPs and drop with volume (€1.30/IP at 50, €1.20/IP at 100, €1.10/IP for a full 255-IP subnet), all with unlimited bandwidth included, while residential starts at €5.00/GB for a 2GB pack and drops to €3.75/GB at 50GB. Two completely different pricing logics for two completely different consumption patterns. Comparing a $/GB residential quote against a $/IP ISP quote directly is comparing apples to a subscription.
What actually eats your gigabytes
Bandwidth on a per-GB plan is consumed by four things: page weight, images, JavaScript execution, and retries, and the last one is the silent budget killer. A JSON API response might be a few KB. A full ecommerce product page with images, tracking pixels, and a JS bundle can be multiple MB for a single load. If your workload renders pages in a headless browser instead of hitting an API, your GB consumption per successful data point can be one or two orders of magnitude higher, and no $/GB comparison between providers means anything until you know which of these two workloads you're actually running.
Retries are the part people forget to price in. A blocked or failed request that gets retried burns GB for zero result: you paid for the failed attempt and then paid again for the one that worked. If a provider's IP pool gets flagged or blocked on your specific target more often, your effective cost per successful page isn't the advertised $/GB. It's that number multiplied by however many attempts it actually took. This is bandwidth cost hiding as a quality problem, and it's invisible on a pricing page.
When a cheaper rate is actually the worse deal
A lower advertised $/GB can cost you more in practice once you count what a dirtier or smaller pool does to your retry rate. If Provider A quotes a lower headline rate but its IPs get blocked twice as often on your target site, you're paying Provider A's lower rate on roughly twice the GB volume to get the same number of successful pages through. Provider B might quote a higher headline rate. Its cleaner pool mostly works on the first try, and that lands at a lower total bill for the same output. This is the buyer's-remorse pattern behind a lot of the "alternative to X with similar price/GB" threads: people are shopping the sticker number because it's the only number they can compare in five seconds, and the retry tax only shows up after they've already committed traffic. At real scale this stops being a rounding error. In one r/proxies thread, a buyer running ad-tech testing described scaling from 200GB/month toward 1-1.5TB/month and being quoted "$0.70/GB for 700GB and $0.69/GB" by their account manager, numbers reported by the Redditor for their own deal, not anything BirdProxies can verify or match. At that volume, a pool that quietly runs 20-30% more retries than a competitor's isn't a rounding error. It's real money every single month, and it never shows up on the rate card.
When flat-rate ISP pricing is the actual fix
Flat-rate ISP pricing is the right fix specifically when your bill is ballooning because of metered consumption on a workload that doesn't actually need rotation, not because residential proxies are bad. If you're running persistent sessions, account management, or anything where the same identity needs to look consistent over time, you don't need a rotating pool at all. You need a fixed set of dedicated IPs. Paying per GB for that use case just means every retry, every session refresh, every extra page load adds directly to an unpredictable bill. Moving that workload to a flat per-IP plan (25, 50, 100, or a full subnet in BirdProxies' case) converts the cost into something you can actually forecast: you know the IP count and you know the monthly number in advance, full stop, with no per-GB metering at all. The trade-off is real too. Flat-rate static IPs won't help you if what you actually need is a large rotating pool for high-volume scraping across many identities; that's still a per-GB problem by nature. The fix only works when the workload matches the model.
A practical framework before you buy
Before comparing any two proxy quotes, work out four numbers for your own workload instead of trusting the vendor's sticker price. First, your actual page weight: pull a handful of real target pages through dev tools or a proxy log and see what a full load actually costs in KB or MB, JSON versus rendered page makes an order-of-magnitude difference. Second, your realistic retry rate on your specific targets, not a vendor's average across every site they serve, since a pool that's clean on general web traffic can still get flagged hard on one specific ticketing or ecommerce site. Third, ask exactly what's included: is bandwidth capped or unlimited, does data expire, are there overage charges, is the quoted rate the entry tier or the volume tier you'll actually hit. Fourth, price the realistic worst case, not the best case: take your expected GB usage and multiply by your measured retry rate, not by 1.0, because 1.0 is the number that never happens once a target site starts pushing back. The provider that wins on that worst-case number, not the one with the lowest headline $/GB, is the one that's actually cheaper.