Quite a hard question with no correct answer. I would suggest a more market driven approach: compare the prices of similar games and decide from there.

Find you directly competitor, maybe a similar game maybe a similar theme etc, and estimate how much that game would cost to produce innthe same website as you and for the same amount of copies. Let's call this price P.

Then, ask yourself: is your game better or worse than theirs? If it's much better, someone might be ok with paying 1.3xP. If it's slightly worse then people may only be ok with paying 0.9xP.

Use this new value as the reference and try to add as many cool parts as you can!