$20 is not a fair price... for YOU! It's a fantastic deal for your customers. Depending on the level of integration with QB, you could be charging ten times that.
Granted this is a QB integration tool, Synergration's AccessBooks RealTime
starts at $199 for the basic version. It only pulls data from QB. If you want bidirectional dataflow, you're looking at $348, as a starting point.
So what is your plan? API? Web Service? Data export?