+2 for the custom fabrication.
You can buy the pre-fitted brands, but they never seem to go in right and just don't look all that robust.
If you have a car that NEEDS a cage, then don't go on the cheap.
In my experience, a good custom fabrication cage (full) will run you $2000 - $3000 depending on how you want it done and where you want it routed.
You are in MI, so I am not sure if you can have it done less expensive.
Here in the DC area, Mitch Piper is the recognized cage guru for road racers.
Here are pictures of the cage work he did for our race team.