college student; versatile bike to use as transportation + low key MTB trails; bigger kid

I do not know anything at all about bikes. I am wondering if anyone can point me in the right direction. I am looking for a versatile bike good for a college student who is using it primarily as transportation in a city, but also versatile enough to maybe handle low key trails (South Dakota) if he wants to go off-road? He's a bigger kid (6'2", 280 lbs.). Budget I guess is ~ $1K. Cheaper = better.