If hes not going to do alot of fast wing shooting, an H&R/NEF(single shot) slug barrel and smoothie combo would be a great & economical deer ,turkey, rabbit combo. I have found that I just cant hang with slug guns anymore and use my muzzleloader in slug zones now but Ive owned a 500, an 870, an M37 and USH(nef) and the NEF was the best (and cheapest) shooter of them all.
A couple of notes, a new gun goes about 200$ and barrels are about 60 -120 $ . The barrels have to be fitted by the factory, and a rifle receiver can be fitted w/ a shotgun or muzzleloader barrel but a shotgun receiver cannot be fitted w/ a rifle barrel, so if you think you may want a centerfire barrel later, buy a centerfire 1st and fit it with shotguns barrels after.
heres a link
http://www.hr1871.com/Firearms/Combos/handislug.asp
accessory barrels-
http://www.hr1871.com/Support/accessoryProgram.asp