We have just gotten into biking of late.
I would agree that looking at some decent used bikes at a bike store would be your best bet. Plus, the people at bike stores are usually more knowledgeable than the people at big box stores. Bike stores usually have better "used" bikes than the new bikes you would find at a big box store.
If his general use is going to be on the road or maybe occasionally on some sort of nature-type trail (ie-paved or maybe compacted gravel)...you know, generally "average" biking, which is what most of us really do...then a hybrid is probably fine, because it can do both worlds fairly easily.
If his general use is going to be hard mountain biking, off road on poorly groomed trails most of the time, bouncing over rought terrain, then you'll need to spend some money on a decent true mountain bike which is more designed to take that kind of punishment.
Based on what you're saying his use will be, it sounds as if a hybrid would work fine.
My bike is a Specialized Hard Rock. It's about 15 years old, a hybrid. I have just put it back into use after having it tuned up. I paid about $300 for it new. It's been a good bike, held up well. I ride it on some pavement, but mostly groomed trails (either packed down dirt of crushed gravel). Occasionally some of the trails have been slightly less than groomed and it does fine on those as well, for short distances. I am what I would consider to be a recreational rider with a little extra "oomph" for exercise.
Some other well-regarded bike names are Giant, Cannondale, Gary Fisher. My DH just bought a Specilaized Globe Carmel, which is a good bike. He's a big man (think footbal player) so he needs a fairly sturdy bike with a strong frame. He paid about $350 for it new, so used you might get one under $200.
But do talk to a knowledgeable bike shop first.
