Craigslist or PicknPull. On CL in the past few days I've seen varous complete Bugs, starting at about $700 with all the bits. You could unbolt the body and part out all the stuff you don't need, somewhat offseting your costs.
I too have been pondering use of the ever-popular Bug chassis, source of various kitcar projects.
My favorites among them include Porsche 356 Speedster (
https://encrypted-tbn2.gstatic.com/i...g_JbaKh27ugYXw) and Porsche 718 RSK (
https://encrypted-tbn3.gstatic.com/i...Bh17qGycqrOOCz), the latter to my eye one of the most beautiful cars ever.
But, the Bug engine is not so hot: Aircooled, it is not efficient, but is noisy.
I wish VW used similar rolling chasis for later TDI cars, or Subaru had chassis cars similarly suitable.