Both my mountain bikes are from the last millennium. One is a 1993 Klein Rascal, fully rigid, weighs nothing and is loads of fun on reasonably smooth trails. Other is a 1999 Klein Mantra, full suspension, and is loads of fun on everything.
I like my mountain bikes like I like my Rovers: old, fun, full of character. Although to be honest, my mountain bikes give me zero mechanical issues - wish I could say the same of my Disco.
But to your question, I'd look around locally for bikes that are a couple years old. I don't know about your neck of the woods, but round these parts there are always dudes with more money than practical sense who buy a new bike every season or two. A recent model used bike could be a great way to find what you want on a modest budget (relative to new, anyway). Santa Cruz full suspension 29ers are wildly popular among my circle of riding friends. I borrowed one and found out why.
The 29" wheel is great for going downhill in a straight line, or for riding over larger obstacles, but once you get into technical singletrack XC terrain all that extra weight and momentum of the bigger wheel becomes harder to handle. There is nothing like a good old 26" wheel for light weight and precision handling. Pushing the bigger wheels around - both in terms of steering and propulsion - is a lot more work. Something else to consider in your old age.
