Is there though? Whom are you protecting yourself from? People who write curl scripts or serious attackers? Surely if someone wants to commit to an attack $5 is completely neglectible amount of money, right?
All you "protect" yourself from is casual script users and script kiddies which really can be solved by IP rate limit. If someone has access to thousands of IPs they can probably afford to drop $5 to solve the captchas too, right?
Having written code to bypass captchas, up to and including Google ReCaptcha: yes, there is a difference. A large difference.
$5 per request is not a negligible amount of money. In practice it doesn't cost anywhere near that amount to call a MechanicalTurk API which will solve ReCaptcha for you. But it's still significant for any nontrivial number of requests, such as in the use case of scraping.
You should adjust your priors here. You're focused on the narrow case where a win condition is achieved by spending n dollars to solve a single instance of ReCaptcha. People who use ReCaptcha are (in my professional experience) overwhelmingly more focused on requiring ReCaptcha to be solved for every individual request of a given type.
I have been in the position you speak of, where I had a revolving set of IP addresses, requesting servers and user agents, and $5 per request would have immediately shut my operation down. As it was, the actual ~$0.15 per request to solve ReCaptcha was sufficiently significant that I couldn't curate enough data for what I needed, despite having all the other resources you mention.
Seems like you really hadn't done your research. Deathbycaptcha has been around for probably a decade now and their rates were always something like $0.1 per captcha.
That's not it though, captchas take profiles, so if you correctly configure your profiles then it becomes even less than $0.1 per solve as a profile might only get 1 captcha per 10 requests.
It's dead easy to get around captchas unless you're just a casual scripter that wants to `wget` that one article - then fuck that guy, right?
Possibly, I no longer do that work. But that was never the price I saw for the service. Cheapest I ever saw was still 10 times that, and requests frequently had to be resent due to spotty completion.
I think people who use CAPTCHAs know that they are protecting their site from script kiddies. Real attackers are going to find actual vulnerabilities to achieve much bigger damage than a script kiddie abusing the "comment" feature to write spam content, or otherwise making a large number of submissions for the webmaster to sift through.
CAPTCHA is typically one of several defences, and you underestimate the cost they cause attackers. One of the main problems for an attacker is not really the dollar cost of buying a CAPTCHA solver, the real inconvenience is really the time it takes to solve on. The attackers go from less than a second to complete a request, to 30-60 seconds to complete a request, a significant slowdown.
All you "protect" yourself from is casual script users and script kiddies which really can be solved by IP rate limit. If someone has access to thousands of IPs they can probably afford to drop $5 to solve the captchas too, right?