I unno, that 2010 GT Avalanche looks to be a decent bike and @ $200 less than retail the price is about right. I wouldn't buy one new for $500 (as that's good low starting price for a real quality used bike), but this, lightly used for 3 is ok.
All of the components are "hi end" generic, serviceable & better than most for the money, but not known for longevity. Suntour shocks for example usually only have a season or two before they're spent (those may be slightly better) and rebuilding them can exceed their value...
...but, I do think this bike is a near perfect platform for the first time builder on a budget, to see what yer getting into & experimenting (down tube is a lil odd, but workable) - it looks it might have double wall rims if just 14g spokes, the frame looks stout and well designed & while the components may not be the best money can buy - it's got exactly what I'd want in a beater trail bike & it'd be easy enough to upgrade later as the need arises. For example, swapping out calipers for quality can be quick & cheap (new Avid BB5 take offs can be had for $20 if you ask around, $40 new w/rotor) - unless you need mounts and hubs & wheels relaced... or a new wheelset too as ya might as well etc., etc.
Even the disk brakes are a bonus - while V brakes work well (unless wet/frozen), the wear rate can be obnoxious for both pad & rim, particularly when you combine the speed & weight of a MB with the mud, dirt & grime of trails. The rear disk isn't a problem as I see it - you can bolt a sprocket in it's place to bypass the problems with the kit "rag joint" (adding rear V brakes ofc) or the cost of an aftermarket sprocket adapter & I really think a disk's mount about the best way to add an engine drive sprocket, can't beat it's strength & that's something to consider if you're geared really low & trail beating.
...but in all honesty, I think you really do need gears to any remotely serious off roading and jackshaft/shiftkit would let you keep the rear disk as well. The 66 has the power w/o a doubt, it's just a matter of making it usable.
I trail ride a
lot on a very basic aluminum mountain bike, motorized with a Chinese in-frame 66cc - I beat on it all winter too, the worse the weather the better. It's defo not a dirtbike by any means, but the 66cc as more than enough oomph to do what it needs to. Unfortunately, it's got a kit 44t rag joint sprocket and that's it's biggest problem as a trail bike, geared too high any technical sections of the trail require an awkward dance of throttle/clutch/pedals & gears to get through it... I've ofc thought about regearing it low - but low enough for trails would make it almost unusable for street... so I tend to ride it on the trails like, well, a mountain bike lol - pedaling the tough bits and motoring the straights.
So long as ya remember the golden rule - that
anything you off road is essentially disposable, that damage is just part of the game as trees & ditches don't care how much the components cost, I do think an in-frame shifter build on a bike like that a good first build for your interests for a comparatively low investment, quite low for what you're getting w/o a jackshaft/shiftkit if ya decide to go the bolt-on sprocket route *shrug* you could ofc have two I s'pose, swapping them out (high for week commute/low for weekend trail play) is a bit of a pain, but still pretty easy if it's bolted to the disk hub... dunno, I've never bothered tho I've a spare wheel lol
