Shopping Cart - Just for Donations?

Hi everyone,

I'm hoping someone out there can help me...

I've been trying to find a really simple (cheap, preferably free) "cart" that will allow the user to enter a donation amount, their CC/personal info, and hit submit and then kick it over to Authorize.net to process their credit card.

I cannot find ANYTHING close to what I want. There are no specific items to sell... it's only for donations, and the amount is entered by the user.

Any suggestions? I know PayPal has an easy way of doing it, but my client has already signed up with Authorize.net and wants to go with them.

Thanks for any help!!!