I've been asked about integrating online payments for church or school websites. Yes, I have done this, but it's not easy. In fact, you might be better off in the short term with another service. Luthernet's long term solution could be great for you, but the intitial setup is complicated, which means it might not be worth the time if people don't give online.
Let's just say Luthernet charges $500 for the system. Since you don't want to deal with online payments, the system would still have to go through Paypal, which is 2.9% and $.30 per transaction. While it's free to have a Paypal account, that percentage, coupled with how much a web developer has to charge, means that you'll need to have a lot of people sign up in order to make your money back.
My church uses a system that charges a $10 monthly fee, then 1% + $.45 for each transaction (bank withdrawal). It's higher (2.75%) on credit cards. Mainly, however, it's only $10 per month, which means my $500 setup fee will seem pricey until you are hooked into several years with that other company. If it doesn't go well, you can quit them, but if you pay for the service from me upfront, you can't unspend the $500.
You may find it strange that I'm giving this advice. Why wouldn't I want the $500? Mostly, I want the client to be happy, and these payment systems can be a little tricky, so I tend to recommend people go for a company that only processes money. You don't really want to have to deal with the security yourself, so let someone else do that. Your web designer is also not as comfortable with these systems, so it's probably best to shop the online payment systems in order to get the best deal.