I own both a SLG-96 (7.62) & a SLR-105R AK-74 (5.45 with Styer hammer forged barrel) from Arsenal. Both are great guns & fun to shoot. The SLG-96 is a milled reciever while the AK-74 is stamped. Ammo is cheaper for the AK-74 but count on cleaning the rifle everytime you use it. The ammo that's cheap is corrosive. As for what LHRGunslinger said:
If you're worried about price you can order 5.45 by the spam can at AIM Surplus.
Well I bought the ammo (5.45) from them in January for $119/can of 1080 rds. The last time I looked they were up $20 more a can, $139. I bought 5 cans back then & glad I did. I don't feel you could go wrong with either one. As a matter of fact, why not buy both like me, you won't regret it.