Pentester for 10 odd years: usually for an external test you would scope it at X days depending on the number of IPs etc. And it should note that an external test really doesn't find much. External is usually £750/day for 1-2 days testing and one reporting. Internal testing (ie. Auditing a domain and all computers attached) is about the same price, maybe a bit more, and takes a bit longer usually. A build review is hardening the server itself, takes about a day and a day reporting. App testing is totally dependent on the app itself (this is where people have a crack at an actual installed web application usually using user accounts etc. And runs a bit more - £800+ per day usually. Specialist stuff (hardware testing, code review (what I used to do), social engineering, hardcore app testing (stuff like auditing bespoke network devices, high frequency trading apps, etc. Etc.)) is typically 1-1.2k a day.

You can get it cheaper but a lot of it - for better or for worse - really comes down to the skill of the individual consultant. You can pretty much halve these prices, but then you'd end up getting stuff outsourced to India and it wouldn't be any good. Depends if you care about the security of your product or just want a box ticked for some arbitrary compliance and want it done as cheap as possible.

I haven't been a tester/consultant for a few years now, but the prices hold up. That being said one development which has happened since I've left the industry is the advent of crowd sourced pentesting. I know a lot of friends who moonlight with these things and are very good at their jobs, and the rates are lower. The name crowd strike comes to mind, but I'm not 100% sure if that was the company or not. I know a lot of good UK based companies (if it's a web app/remote then the physical testers location doesn't matter) if you needed.