How much do they pay per captcha?
I've checked their website but it doesn't display payment information or prices for the PPM conversion. You have to log-in to the member's area or contact the developers of the website/service in order to find out those details.
However, I would be very precautious if it's required for you to pay something. Use PayPal at all times because you can open a dispute if you get scammed.
For 1,000 captcha u can earn $1 and that's a lot of captcha's to do , so it really takes time to earn that much , esp., if you're internet speed is not so good, so It really does takes a lot of time.