Replying to Need a new mountain bike

I search barred but couldn't find any threads worth reposting on and digging up.

Here is my predicament
I taught mtb at a summer camp last year on a 2000 specialized hard rock. it's 12 years old now, and I rode the absolute shit out of it. I need a new bike. The terrain is fire roads, two-track roads, and some (not a lot) trails. No singletrack. The riding sucks but money for mountain biking is fine by me. I guess the bike suited for the terrain would be a cross country bike or something, not sure. Could I get any money at all out of the hard rock?

Help me pick out a cheap bike suited for the terrain. Plus k to all replies that are stupid. thanks for reading