rowdyrandy
XS650 Enthusiast
How much it will cost to make reliable has a lot to do with your abilities, patience, time and resourcefulness. Does it have good compression, and can you shift through the gears? If so, then you have a good start. You will likely need at least a new cam chain guide, carb boots (JBM), carb diaphragms (JBM), carb rebuild kits, possibly jets, fuse block (modern blade type because glass fuses suck), master cylinder rebuild kit, caliper rebuild kit, brake shoes and pads, drive chain, tires, spark plugs, stator brushes.....
I don't say that to discourage you, but to give you fair warning about what it takes to get an old bike running reliably. If you do the work, these can absolutely be a reliable form of transportation that you can hop on at any hour and buzz away on. I would not recommend any 30+ year-old vehicle for those not mechanically-inclined.
+1 on this. Do your homework and don't get nervous in front of the buyer and "just do it." I don't know if it would take all of the above but be prepared...and even if it does it's still a good deal imo...people these days will drop $300+ on a phone for gods sake..buy the damn thing, spend a winter getting your hands dirty and come out of it a better person with a kick ass bike you can be proud of. Mine has given me my fair share of grief over the years but all have been things related to age.. once the run, they run and you'll feel more and more confident knowing you know this thing inside and out. plus, we're all here to help. good luck.