what bike for me?

We are not in a position to buy a new bike for me yet but I am getting real serious about riding and my current ride is an older, kinda messed up bike. It's a mountain bike, 21-speed. I am looking to be an endurance rider. I want to be able to pull big hills but ride far. So far, this bike seat is killing my bum!
I have a bad hip and it's been hard on the hip, although I can tell my hip is getting stronger. My bum hurts so bad when I ride, it's distracting.

I really don't know anything about bikes or what I should be doing but I'm trying to learn. Any advice/ideas on what kind of bike would be good for me? What kind of seat should I use? I don't have the money to invest in anything really expensive, so good affordable choices please.

Thanks so much for any tips/ideas.

An easy way to reduce saddle pain is to invest in a pair of padded shorts :) They might run you $30-$50 but it'll be totally worth it. Also, if you're having hip pain while pedaling, maybe your saddle is too high? Have you ever had a bike fitting? These guys can adjust everything down to the millimeter to make you as efficient and pain-free as you can be while riding.

Thanks for the tips, will try lowering my seat. Also, where do I get a bike fitting? A bike shop?

Measure your sit bones, then measure the saddle of the bike.

If your bones are wider than the saddle, there's a good chance that's the major source of your bum problem!

There's an excellent book that many of us have, you might want to get it for a reference: Andy Pruitt's Complete Medical Guide for Cyclists.

Edit to Add: visit the Saddle forum for all kinds of info on fit http://forums.teamestrogen.com/forumdisplay.php?f=36

+1 for a bike fit and measuring those sit bones. If your saddle is too wide, too cushy, already too padded, padded shorts are only going to make the problem on your bum worse. My saddle fits really well, and I prefer a very light chamois in my shorts - my triathlon shorts are perfect! hardly any padding at all, just enough to not be abbrasive, and allows my saddle to support me.