Here is the basic structure of how to do it:
set variable #001money_held = MONEY
Text: Stay the night? (Costs: cost,,you have \v[#001])
Choice: Yes/No
Case: YES
CONDITION BRANCH: if #001money_held >= cost
transfer player to the room,,full recovery,,change money (subtract cost).
else
Text: You don't have enough money
Case: NO
Text: Fine then....