Do the math’s. (1,000 x 50USD) = 50K gross p/month. Total volume? Do they plan on say 12 months of production? (12 x 50K) = 600K.

Plus...

1. Estimate how much profit they would make from the total volume.
2. What are the risks involved? Sure winner or big gamble?
3. Are they doing you a favor by offering to purchasing the design?
(is it really that good)

Out of interest, the guy who programmed PAC MAN for the Atari 2600 received something like $20K for it. Atari made something like $5M profit.
Atari took the risk, but Atari should have also paid royalties after discovering the success of the game. In my opinion, he really desreved about $250K.
(He was not an Atari employee, it was out sourced)

Best Regards,
Trent Jackson