It is a sad fact of life that good things cost. You can use float (window) glass and many of the experiences learned can be transfered to fusing glass with appropriate changes in temperatures. You can also look to buy cullet from other workers. These will be small pieces, but can be built into larger pieces if wanted.
There is a cheap fusing glass called Baoli (Bao Li) made in China. It gives a range of compatible colours for fusing. I have also heard that that an American company is or has come out with something less expensive than Bullseye or Uroboros – don’t remember which, as I’m not there.