A good source for riding techniques can be found at the Trials Training Center website:
http://www.trialstrainingcenter.com/
Click on the button "how to ride"
Trials Central is great trials site for information, competition results, and community forum:
http://www.trialscentral.com/
Back in 2002, I bought a used 2001 GasGas TXT280 and rode it for several years. Where I live, there were no good practice areas (other than my backyard). My only real practice was during competition events, which was really fun due to the great sections. Unforunately, with my family constraints, it was difficult to spend an entire day traveling and riding the event. I ended up selling my bike last year and miss it a lot. Someday, I will buy another.
Trials is a fantastic sport and great for cross-training. Prior to getting my XC250, trials was the only thing that I rode. When I got my enduro bike, I transferred all of my trials skills (like log hopping, throttle/clutch control, balance, etc.) and immediately was at my friend's riding level. They could not believe that a "newbie" to enduro was riding at their level. Even today, I will be the guy to try larger obstacles on the trail (like hill climbs, logs, etc.) because I have the confidence from my trials experience. There is a reason why David Knight and Juha Saleminen are top riders... both have a trials background.
Regarding a bike, I would buy a used one from 2001 to present. Things are pretty much the same since 2001. Early bikes (before 2000) were still developing too much into the modern versions they have now. All brands are very good. You can't go wrong with any GasGas, Sherco, Montesa, Beta, or Scorpa. GasGas and Sherco are at the top on my list due to the parts availability and support. For GasGas, I would go with a 280TXT or 280/300Pro. For Sherco, I would go with their 2.9 model.
You should be able to get a good used bike for $2500 to $3500 depending upon the year. None of the bikes will be "beat" like an enduro bike from an engine standpoint. Just expect to see lots of body damage like dents and scratches... which are war wounds and give the bike character.
