Your stated use suggests something like what the 3 gun folks use.
Check that out at places like 3gunnation.com and the multi gun section of brainenos.com for ideas.
It looks like suitable versions of the AR are priced in the $1200 to $1500 range.
Walt Kelly, alias Pogo, sez:
“Don't take life so serious, son, it ain't nohow permanent.”