no one does cages like they do. they are FIA certified and tested amazingly! unfortunately, there are no places that do prebuilt stuff. you might as well just go custom. I was looking into CCs a while back, they are about 2k, and you have to send over a piece of welded structure back so they can verify the welds. u can have a sick cage welded in for about 2500. i've seen them for as much as 4k, but the average is about 2500. Davenport racing makes a good cage, and i have 2 friends/buddies that can do cages and have built several for rally america. AFAIK, Targa doesn't have to Meet FIA, i thought it was just C.A.R.S. logbooked. but you can still get a custom cage made to FIA specs.
There are different stages^^ street,competition. If its made of the right spec OD wall thickness per the rules a bolt in can be welded in. Im sure the company can give u weld plates vs a bolt in style give them a call