You need to run a check immediately following the take GP code, this bit needs to be checked:
1BE B7:6 Not enough money
So right after the 85 XX YY, you would input the check like:
C0 BE 81 XX YY ZZ
If byte 1BE is set (not enough gold), go to address XX YY ZZ (wherever or whatever you want to happen if not enough, like a "not enough GP..." text box).
Your code after this check would be if the party does indeed have enough, so the event progresses.
1BE B7:6 Not enough money
So right after the 85 XX YY, you would input the check like:
C0 BE 81 XX YY ZZ
If byte 1BE is set (not enough gold), go to address XX YY ZZ (wherever or whatever you want to happen if not enough, like a "not enough GP..." text box).
Your code after this check would be if the party does indeed have enough, so the event progresses.
We are born, live, die and then do the same thing over again.