I was in your shoes about 3 months ago...except a kx80- 94
You either are going to get a bike that needs alot or not and it depends how mechanically inclined you are and then how much money you want to put in the thing...I looked before I went and found you can get parts-oem from multiple sites, and i quickly found my favorites, oh and then also spending about 20 hours reading forums and figuring out on how to fix the thing.....I only bought this bike so I could putt around with my oldest boy, I picked him up a fifty, And also not a pity party but just what I've had to so far, maybe a little over board, but I figure it'll be his in 2yrs or less.
First I got a Clymer manual and started working on it.... Mine did not run, got it for $100....had to replace piston, rings, top bearing, pin etc., replace the transmission fluid, flush the rad, new spark plug, clean the air filter, reoil it, get a new gas can and some oil and that's the real kicker...oil for 2 stroke...if you look you'll get 30 different opinions on what the best it from 20 different people....previous owner on mine used standard non synth on the bike with a ratio of 40:1....when it should of been 32:1 per Kawi. I debated on this and went to Bel-ray H1R for the mix and for the tranny....contacted Bel-ray and he wrote back and told me what ratio and tranny oil weight to use......Got the bike running....won't shift right and fouling plugs like crazy....now you become an expert on jetting....plus my bike has a fmf fatty and Boyesen Rad valve(which I had to send pics to multiple people and then Boyesen helped me alot) so wrote them and asked there recs on jetting...fmf has it posted but Boyesen wrote back....Onto the tranny....replaced the cable, clutch discs and springs, the pusher shot and the actuator very worn and relaced the seals and bearings on the cover. Now it shifts fine....Which I just finished last night!! I forgot to mention the previous owners son let it sit outside so both brakes were totally seized, had to buy used off ebay and rebuild those....
Not to mention both tires are hard and dry rotted and the front and rear bearings need replaced to, got the front bearing kit....gonna wait abit on the back....when i do it I'll replace the sprockets and chain at the same time, along with both tires....and I forgot....have to replace the gas tank too...leaks at the very top can't fill it too high. (breathe)
So if this all sounds new to you, not trying to scare you away, but you just don't know what you're getting, especially if you don't know what your looking at.....and I haven't even touched the forks or the shock and all the bearings on the frame, swingarm, linkage, yet either. All in all what I've learned 2 strokes are so easy to work on, BUT you have to do top ends every 40-50, hrs depends who you talk to. Hope this helps