Ask HN: With First 50K free, Is this the best payment solution?

I'm working on a solution which lets users pay their 30$ bills and charge them a dollar for it. With Stripe.com they would charge me 2.9% + 30 cents which will take the overall charge for end user to 33-34$ and user might think of not using my services and pay it themselves. This seem to be the best bet for me. Any thoughts on how a startup with this model might keep the costs low?