Since Feb.2003, under the present interpretation of the CT "assault weapons" ban, the CSP says (for now anyway) any NON 7.62x39mm semi-auto Kalashnikov style rifles are legal.
However, if you choose to build a 5.45x39mm rifle, you will be using a newly made, stripped receiver from Ohio Ordnance, Rapid Fire, Ewbanks etc... Because these receivers were made after Sept 13, 1994, the rifle you build will have to be neutered. Otherwise, under CT law, you will be assembling an "assault weapon." You CANNOT have on your build a bayo lug, threaded barrel, flash hider, and the muzzle brake must be permanently attached.
So, what you are left with is essentially a Romanian SAR2, CUR2, MKII, WUMII. When I picked up my 5x45x39 rifles, they were in the $300 price range. Price wise, it just didn't make sense to build.
Figure $60-65 for stripped receiver, $200 for U.S. compliance parts (stock set, pistol grip, & trigger group) plus labor if you are not doing the build.