Mine is a Tristar Tec-12. Cost $550ish new. Got more as a shoot anything I want to throw at it gun. Thought it would be a bit of a poor man's SPAZ shotgun, and I suppose it is. Once someone figures out how to put a mag extension on it, I will do the same. They allready have for the straight pump and semi versions without much trouble.
But, for a straight combat stlye Semi, a S12 is the way to go. I liked mine, but could never get it to shoot cheap brass without cycle issues.
A Mossberg 930 SPX might be a good option, but have never shot one.