$5k might be fair, who knows? $5k total? per store? Does that include future installs?
Are you selling the source code too or just the compiled application?
If you're not selling the source code, are you going to license the software to him based on the number of installations or just give it to him for a specific price? You could sell it on a sliding scale based on the number of installations. If he has 22 locations and 5 installs per store, then have pricing for single installs and discount for a pack of 5 licenses.
You shouldn't give it away cheap just because it "wouldn't be too much trouble". Take into account the impact on business. How much time & money will your software save them? Remember time _is_ money.
Good luck.