Paypal send cash script

Hi there, We are currently building a platform which provides several payed services. Now we need an easy way to have our customers deposit money to our paypal account in order to raise his credit balace with us. So we thought paypal would be a good way to do so. So basically what the script should do is: 1) Provide a form where the customer is able to fill in the amount he wants to deposit and will then be redirected to a paypal screen within our page. There he can send the money and will then be again returned to his credit balance page on our site. 2) Secondly the script should be able to check wether the amount really arrived at our paypal account and if it did will update the credit balance of the customer in a mySQL table adding the amount he payed to his credit balance with us. Basically shouldn´t be really hard to do. I guess there are even some free classes out there, that can do that. We don´t mind if you use such a class as long as things work fine (and price ain´t too big). Finally in case it´s easy doable other payment options like credit card would be cool, allthough not really needed.