After a short thinking, I come up with the following suggestions:
1) Claim down, I know its stressful and frustration but really nothing can't be solved , we just need to find out the solution.
2) Reduce CPU usage, some features could be temporarily removed until we could afford the server we want, eg remove some of the regeneration counters like explore points, or make longer regeneration time with proportionate regeneration, or put things into several servers, eg a main server, an image server etc... I'm not a computer expert so you might know better.
3) Use ads... might help the income a bit? With the current active players the revenue wouldn't be great, but every bit helps.. I hope.
4) Stop getting new players, if there isn't a long term solution yet, keep getting new players won't really help (as CPU usage will keep rising) but might give them bad impression and turn them away.
5) Change the way things are acquired in MDshop, as you mentioned above, increasing the price might not help, but you could add additional precious items with higher price. But I think it's better providing items in a temporary basis is a better choice, like a pass lasting some time which will grant you 2x regeneration values or items/features that will last only a week. This way you could guarantee a more stable revenue. (btw im not a donator, don't cure me -.-)
Hope you find it useful.