I really never do any SCCA/Road Racing, so if I bought a roll bar/cage, then it would just be for drag. The problem is, are there any out there that are relatively light (under 100lbs)?

Where to get them? anyone have more info/pics?

 

Check the rules for whatever organization you want to run. 1.75" steel tubing, the designated thickness (1/8" I think) is about 2 pounds/foot. Unless you are running a rally car, you should be able to easily make a full cage with reinforcements for well less than 50'.
If you have access to a TIG welder you can use chromoly (more $$$) and save approximately 1/3 of the weight.

Ben