Use PayPal for the ordering. Low overhead and quite easy to use for simple product payments.

Note: If you begin selling a product, even for 5 bucks, be prepared for a lot of technical support emails. IF you provide the source code, be prepared for even more emails. Also, you may be liable to support it for a period of time depending on your license agreements. IF you don't set up a license agreement the purchaser could sue you if the product fails and they lose money on their software. Beware of all the risks involved.

Also, if you are selling this personally without a company front then you could be personally liable. The risks of business need to be weighed.

Good luck with your venture, just be sure you are prepared. I still like to deal with a handshake, but the internet has changed that. You don't look your customer in the eye anymore.