2captcha is about 0.0005/solve, give or take do to their failure rate. There are other services as well and pre-paid bulk purchases lead to lower pricing. I wouldn't want to ballot stuff the crazy number that is the combination of all Visa credit cards but for much smaller problem spaces 2captcha and others are very reasonably priced.

Can be had much cheaper, especially if OK with a non-zero failure rate (and/or bit more latency). Note that my hands-on experience with this stuff is now relatively dated, from a "prior career" -- coming up on 10 years now, even. If anything though, then I'd guess that it's become cheaper over time, not more expensive.

Look again, that is per thousand captchas.

Still pretty expensive if you wanted to do every single Valid CC #, though.