Not cheap and not easy. Old beetles may come cheap for the chassis and the stock engine, but to get enough power to drift your going to need some money. It only takes 100+hp to drift, but even a 100hp engine can cost $1000 to build sometimes. Not to mention that they are really hard to keep control of when the rear end breaks loose. They are harder to drift than an MR2. All the weight is in the back of the car, so it will grip well until it finally breaks loose. And when I say break loose, I mean break loose. Its really hard to countersteer for that much oversteer that fast.

That hasn't stopped me from wanting to build a Beetle, but its not going to turn out to be a drift car. I'm actually working on one as a project with my dad.

EDIT: Forgot to mention that the front ends of old Beetles like to lift off the ground at higher speeds.