i like litecommerce(very easy to use & customize) by the makers of xcart you can use netbilling as a processor and netbilling only charges 99$ to set up an account. Im going live with an adult store in a couple of days
http://www.litecommerce.com/
99$ + any extra modules you wish to purchase
it comes with a lot of good ones for free... but for additional functionality like the ability to run an affiliate program or advanced promotions (buy one get one) type of stuff then its extra money but for the most part you will only send about 150$ total rather than close to 300 to get similar functionality via xcart
hope that helps a bit
