You may think $10,000 is lots of money but people going to just laugh at you and it's pocket change to them who owns it and people who owns the vehicle that is not Ecto replica.
To give you an idea how much those cars are worth, just the vehicle itself in a showroom finish is going for more than $40,000. A 1961 vehicle that was used for display as an ambulance at a race track was going for close to $7,000 and it may have gotten to $10,000 if he didn't took it off of Ebay early.
Once you get the vehicle, you may have to restore it. Than you have to get all the equipment which does not come cheap.
It's also not cheap to maintain it either and the parts are expensive since it is hard to get.
If you only have $10,000 to spend, I recommend just get yourself a 80's or 90's wagon and make that into an Ecto. In fact, someone got a free wagon and he made it into an Ecto. It's not that bad looking either. He did a good job on it.