Originally Posted by LeeG

Billy, I have no idea what the used bike market is where you live but I suggest you refine your intended use. If you're new to mtn. biking and touring I'm guessing you're new to bike mechanics and don't have a tool box of bike tools necessary for swapping parts and repairing/rebuilding wheels of used bikes. If that is the case and 500 is your limit I'd suggest buying new and riding it into the ground as you develop experience. If you don't have the tools and skills you'll easily pay 50% more as you acquire specialized tools, retail parts and retail shop labor.

You are much more likely to have trip stoppages from all manner of failures than frame breaking. There is nothing wrong with aluminum especially if the majority of new and used bikes are aluminum.

An old mtn bike will probably have a cheap shock that is no longer serviceable, if you're replacing it with a solid fork with mid fork eyelets and a new headset the price just jumped up. The old steel mtn bikes mentioned will work great, if they're in your market.

What are common brands of bikes where you live?