Vic, try for a used hard tail. You should be able to find a decent XC hardtail ride with that budget. Those are typically light and climb well. They should also be a little less expensive than their full suspension brethren because there's no extra components to pay for in the back.
Models to look for used:
Trek Superfly
Trek X-Caliper 29
Giant XTC
Anything similar to those. Hard tail. Disk brakes. Suspension fork. They'll be relatively lightweight, they'll pedal well. Only downside is hardtails get a little rough because you are the suspension. But in the mean time, if you can keep borrowing your buddy's bike, do it! Borrowing=free MTB!! But don't get hooked on the nice parts.
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TnNinjaGirl welcome to the discussion! Your mistake was telling me about your biking stuff
now you're roped into this thread.