At my last look, 870s were listed in .410, 20, didn't even look for 16 & 12 (& forget if in 10). They run the gamut from the Express (yup, they're a bit rough but ~$200 new if you look around) to as fancy as you could pay for. Also 3.5" (wish I had one) & youth models which is really neat for the vertically challenged.
I use my wife's youth express for quail & doves sometimes & it's quite a bit lighter than the 12 although the shorter stock takes some getting used to.
For ~$200, get a few.