For full contact racing, check out the Australian V8 Supercars series. Those guys really go at each other within the rules in high powered machinery. Not like the whimpy fragile German V8 racing in DTM.
I've been in a few spec SMs. They are surely fast in tight tracks. Operating costs look good but also depend on how silly you want to be I guess. Some of those guys shell out lots of cash for 3-5 more hp. Not saying one would have to do that, but it seems it is possible to spend money if you think that'll get you the 1/10ths you need...