Pipe is for plumbing, conduit is for elecrical, and tube is for structural. I think 1.5" tube is a bit on the small side for a fullsize cage. It is fine for support, and gussets, but the main structure should be something bigger.
As for benders, look at an M-Tech or JD2 (same design). There are plenty of benders to choose from. A complete tubing bender will set you back over $500 to start bending one size of tubing.
Also a roll cage is the worst project for a beginner fabricator.