USD 10 per bag per day (so not cheap). Available in both Terminal 2 and 1 (presuming you are flying DL ATL-MAN you arrive in Terminal 2; AA arrives in Terminal 3 which is connected to 1). More info is at http://www.manairport.co.uk/web.nsf/...uggageArriving
BA departs from Terminal 1 and if this is a separate ticket it has the short-haul baggage allowance (typically 20kg or 44 pound limit, not the 140 pound limit that you get trans-Atlantic, so storing the bags at MAN could save you a few hundred dollars).