Best shopping cart plug in if I have a custom theme?

hi,

I was just wondering if there is a good shopping cart to use with a custom html site. The site is https://www.sevenbarfoundation.org, and I need to sell some tickets on it. It really isn’t anything fancy. I just want something simple that will direct them to paypal to check out and allow them to pick the number of tickets that they would like to purchase. I was installing WP e-commerce, but it seems like it changes the theme of the page.

Any help on this subject would be great. I can clarify more as well.