I say go for a rigid (no-suspension) steel framed mountain bike. The Trek 800 and Giant Boulder are both in your price range and there is probably a bike shop near you that sells one or both. They might not look as flashy as the bikes Target has, but trust me, they will take far more beating and last you a lot longer. Make sure you have the shop owner help you figure out what size is best for you. The right size will help you get the most joy out of you money.

As far as what a good bike costs now adays, that depends on the rider. You're looking at the lower end, but still a far cry better than the generic rides. At the other end, there are full-suspension bikes that sell for over $4000. Obviously, those aren't for everyone.

Ask any more questions that come to you and let everyone here know what you get.