that is a loaded question,a s all comes down to your budget and what all you can fix/upkeep yourself and what parts you have access to
if you want a sled to jump on and just ride, and NOT worry as much about things being worn, and soon needing ???
NEW is the only route here and even then new things fail
under 2k would be my prefer deal on used sleds IF all else seems good
as top ends, skid bearings and such, all start to be in need of TLC IMO after about the 5 k mark IF you get there
and after 3 k, about anything can happen IMO depending on how well the sled was cared for or NOT
average miles per yr in MY area if you a die hard is maybe 1,000 a yr
at 3 k, that's 3 yrs of riding (shocks can need rebuilding pending if JOE racer owned and rode it, or if it just a much older sled thats been sitting long, time isn;'t always friendly to things that sit)) and storage, and storage is a BIG part of s used sled
heat drys things, mice eat things, sun can be a killer, not washing off road salt or ??
real easy to pretty up a beat up sled to make it LOOK good on the outside LOL
buying used is always a gamble IMO, unless you know who owned it and HOW they cared for it
so as I said, its a loaded question that tends to be based more on how, and how it was cared for , than just miles alone