I think you'll find that roadies -- guys who ride road bikes -- will tend to suggest hybrids, while mountain bikers will recommend MTBs with slicks. It comes out to tyhe same thing in the end. If you see yourself riding almost exclusively on pavement, with occasional excursions on groomed hardpacked dirt trails [in parks, etc.], a hybrid would probably be a better choice; if you see yourself being more adventurous off-road, you might want to consider an MTB. Either way, you'll have a decent bike.

As for cost... I think of $3000 (US) as an EXPENSIVE bike. $1000 is an inexpensive bike, and anything from $1200-$2500 is "affordable." That's not everyone's range, but the truth is that you can get a pretty good, even race-able road bike for about $1000 these days. Start with the hybrid... if you like cycling and you want to move into the roadie world, start saving. Incidentally, cycling is probably the best exercise for losing weight. Period.

BTW, I have a friend who thinks of $4000 titanium bikes as "affordable." I guess it's one of those perspective things.