In my latest Git update I made money items worth more so there is less chance of running out of cash, I will try to come up with a solution in case the player runs out of money, so that the player is not getting completely stuck. For now you can just cheat yourself money by entering "Give Material 10000" on the console until a proper solution is made.
The shop menu can still be interacted on delta touch with the virtual keyboard arrow and enter keys.
The crystal drops are inconsistent because the code behind it is complex, I need to refactor it so that crystal drops are more generous.
Edit: I added a emergency cash from the shop menu which can be used once per map. Should give you some credits which allows you to buy some of the cheaper stuff till you looted more cash.