Engine swap 99 dakota. v6 to v8?

Well I just threw a rod in my 99 Dakota 3.9 v6 4x4 I just bought friday. Gona need a new motor. Don't really know much about swapping engins but I want Somthing with a little more power but not to much to wear I can't afford to drive to work 4 days a week. Would the smaller size v8 just plop on in their? How much worse on gas would it be if I had Somthing even bigger put in? And last but not least, know a good places for cheep engins? Any advise would be really apriciated even if ur not sure its good :) Ty!