I use CoolTrade and they have 300+ indicators. If that's not enough, you can go to their community board and request additional indicators. They're pretty good about adding them.
I've done good deal of work on trade-ideas API, so I can easily do it if your scan can be broken in 2 phases where TI generates the primary scan and then we run secondary scan on the TI's result. This solution won't need huge machine and costly data feed. If you are planning to have realtime tick by tick market scan; think again. It will be very costly to develop and run. $10k+ easily... Then also god knows what will you get... Someone I know runs multiple instance of stockfinder to get same. Three huge computer, three subscription is big hassel. But who careslid you make money out of it.
Madscan claims they WILL do custom alert/filter programming on their website, and in correspondence have said that it will cost anywhere from a few hundred to several thousand dependent on the needs of the customization. So maybe enough people have bugged them to start this? i switched from trade-ideas to madscan because madscan is willing to customize. Though I have some issues with it being incomplete compared to trade-ideas.