Air-rifle competition distance is 10 meters (33ft).
Some suggestions:
Make provision for pellet splatter to keep cleanup after shooting simple.
Remember that airgun power can vary considerably. Reusable reactive targets will have to be tested with both ends of the power spectrum to make sure that the powerful airguns don't damage the target and the low-power models will make the target react.
Be sure to carefully explain the power limitations of the target system to prevent misunderstandings--e.g. "6ft/lbs @ 10 meters" or "up to 20 ft/lbs @ 5 meters".
You might want to add a way to shoot boring paper targets
some folks do postal matches, want to practice for various types of competition, etc.
You'll have several markets:
The "Wal-Mart airgun" crowd
The "airguns are only for practice" crowd
The "hardcore airgunners"
The first crowd might be willing to spend $20 to $30 for a product. Probably less.
The second crowd MIGHT spring for a $50 product if it's obviously very nifty.
The third crowd will pay almost anything for something that works well, lasts a long time and is really useful.
There aren't many in the third crowd... Most are in the first crowd.