I think it would be nice to allow for more ways to obtain coffer keys. It seems like a lot of people are divided by either liking skilling or pvm more. Would be nice to add them to those respective shops.
PvM shop could have key for: 50k (not too low that it's easy to get a ton but not too high that it feels like a waste of pvm points compared to the 30k pvm box option which is popular)
Skiller shop could have key for: 5k points. I think this might be fair. Non-donators would take longer to even reach 5k. Even high donators with more points per 1m xp would still take awhile to get 5k. (Especially when they're already 5b xp >_>)