CMH is a circa 1998-2002 Match Target Match HBAR. 20" HBAR A2, no bayo lug, may or may not have a flash hider or a compensator is about the only options that I know of. Pre 2000 will have the small Colt doublehead screw and be undrilled for detent, later will be drilled but most still have the screw. $700 is a good price
Colt markings should be on the barrel C MP C 1:7 NATO or similar, CMB marked A2 upper, C marked half circle carrier and MPC or MPa letter then C marked bolt
ETA: $700 might be low, they are getting scarce, but definitely less than $1,000.00 for that particular type Colt. They are great. I own one and had another.