Which Payment Processor Should I Use?

I am about to launch my new site, it´s just a few days and it will be all public. I think that I will do sort of a silent launch. I will then launch it and publish information about it here at my blog, this will be the only launch. Then I will try to find out if everything is working ok, and fix the problems that it might have. After that I will start promoting it with various online marketing campaigns. My logo is ready, the design is ready, my categories are ready, today I am looking at payment processors. I have mostly been using Paypal and I think that Paypal can be trusted and it´s easy, they are probably not the cheapest processor and they might be hard to reach regarding support because they are so big. But at the moment I am thinking about using only Paypal. I have been looking at a few others as well, and especially 2CheckOut, WorldPay and Authorize.net. The problem with the other payment processors are that they all cost money to start using, they require a setup fee. And when you start a business you want the expenses to be as low as possible. So, I am thinking about starting with only Paypal as the option for "advanced members" and when enough registers and I think that it´s time to get more options, I will join another payment processor. But I am not sure that this is the right decision.