As most people have said, PayPal is incredibly easy to get started. I am still using their website payment standard which involves no coding to get started taking payments.

You'll need code later for doing IPN and customizing and encrypting the buttons. But it is definitely the lowest barrier to entry. It is also probably the cheapest option, at least when starting out.

I added Recurly for credit card payment for flexibility and credibility. The costs are much higher per paying user than PayPal. Each credit card authorization costs about 30cents, and if a customer input bad credit card info and you have dunning on, it can cost more than a dollar to have a nonpaying customer.