I just went and looked at a couple of U.S. based suppliers. Cheapest tubes/lugs were at framebuilder supply. Columbus Cromor is really cheap, but chainstays and seatstays really add up. So you could just make a couple of main triangles.

I feel like Joe Bringheli could put together an inexpensive practice kit for you, but I haven't heard his status recently. Last time I ordered from him was a long time ago. He went out to the shed to look at what he had in stock and called me. I bought a batch of Zero Tre from him for practice, enough to get a quantity discount.

If you want to ride your first frame, put something really valuable in the top tube to motivate you to cut it up. I would say your wedding ring, but that might cause trouble. Maybe just a stack of Starrett hacksaw blades?