http://www.jmbsoft.com/software/tradex/
- Affordable ($400 unlimited domains or $70 per domain)
- NOT obfuscated or encoded source distribution (so if you know PHP, you can read the source code, code is clean and a good read)
- Incredible fast support via the forum
- TradeX doesn't require a database server (no MySQL required, optimized for speed)
I'm not affiliated, just like the programmers products and services very much. Had some issues fixed in days, sometimes hours (snapshot releases). Good support, will even install the script (for $30), but will also check your site if you mention any issues. Discreet with your login info if privately provided.