Someone had a Mossberg for sale in the marketplace here on BS the other day.
I'm getting my son one for Christmas this year and decided to go with a true AR for the build.
I'm building from a Palmetto stripped lower for mine, $49 (no longer on sale) plus Palmetto lower build kit for $100.
You can get a PlumCrazy lower for +/- $140 plus a CMMG .22 upper for $350 and have the ability to add another caliber upper later.