First thing on any used dirt bike is to expect to buy new front and rear wheel bearings. Most likely the headstem bearings are neglected and will need to be replaced also.
now the rear end, check the lower shock bushing! If there is any play, the unitrak arm there is about $100 then add about $170 for the rest of the rear end bearings you will need. As most likely if one is bad, all are bad. So have someone lift the bike off the ground as you inspect all the bearing points in the linkage. Also check the swingarm for side to side play.
Other than that, expect to maybe do a top end build here in a few months of riding if the top end is still good. you may also need to do a clutch job, reeds, forks and some cables may need replaced.
Last sticky thing about MX front and rear calipers, see if the pins are stuck in them. If they are, check the pads. If the pins get stuck, some people do not replace the pads and thus chew rotors and other parts.
Hope that helps a little