I bike everywhere..so I have a nicer bike with all sorts of toys. I like hybreds with lots of speeds and 26 inch wheels instead of road bikes for comfort and the tires are wider...and the handle bar width is as well. (more stable and I like going down hills really fast)

Many people buy bicycles with front suspension because they think they are cool. They are made for downhill racing, not riding around town or road riding. Many people buy bike seats with springs in them..or very soft seats..you are begging for back problems if you are going to do any amount or riding..Get a nice firm seat. I have a Terry seat that is women specific and i love it. Also get road tires or touring tires and not knobbies if your planning on riding on bike paths and roads..it's a much better ride.

If you start riding a lot I would suggest spd of some sort of clipless pedals and cycling shoes..I have dual sided pedals that can be used with spd or regular shoes...

Standing and riding up hills (climbing hills) is not bad for your knees if you are in good shape...it's actually a really great way to work your quads.

As far as a fancy bike or a cheap bike. You get what you pay for...but you can often find a nicer bike used..just make sure it fits you.

Hope this is helpful.