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.