The correct option is D ever since
The context refers to a situation prevailing after an action in the past (I bought a new house).
"Although" in option A is incorrect as 'although' is used to introduce a statement that makes the main clause seem surprising. This does not concur with the context.
"When" in option B is incorrect as it is used as a relative verb while referring back to a noun and introducing a relative clause. This also does not concur with the context.
"Because of" in option C is incorrect as this prepositional phrase is used to give the reason for an action. Here, the context is informing us of the time period since I have been short of money, but this is not necessarily the reason for being short of money.
"Ever since" in option D is correct as the phrase is used to indicate the duration of whole period of time since something happened. Here, it refers to being short of money since buying a new house.
Thus, option D is correct.