That does make sense to buy one already done, but one of the main reasons for the engine swap is to take on a little project. Being as the 12A is going to be a N/A I should imagine that will keep the costs down, no turbo, computer, intercooler ect, and less fabrication costs on labour.
I would look at putting some money into a engine rebuild by myself and for the porting obviously not by myself :)
All of the bodywork and paint I can do myself.
I will have to look into the engineering side on the 12A because I dont want to do the engine swap and find out I cannot get it registerd :(