That is absolutely ridiculous
String him along and tell him to procure the part while you procure financing. Do not pay them a dime.
Frankly, if they have done work on the top and there was never a leak before the work, I would argue that the work they did caused the problem and they should be fixing it at their own expense. Get corporate involved.
Have you done a drench test? Take a garden hose w/o attachment and let it pour over different parts of the car with someone inside checking.