It goes something like this…
I have a 19__ (insert moto brand), that I need to get on the road. How much will it cost?
Write that question a couple different ways and you will have what I am asked most often. Roadworthy to me and roadworthy to you, may be very distinct. Here are some essential things you need to consider when getting that old bike on the road. Most of this stuff is easy to accomplish at home with some patience, a good reference book or two, and asking questions in an online discussion group for the make and or model of your bike.
Tires - $150 to 300 - shop You have two points of contact with the road. Make them count. Are the old ones in good shape, do they have tread, are they dry rotting? And, since they are your only two contacts with the road, don’t be a cheap ass.
Cables - $20 for each cable - DIY They may work for now, get the new ones anyway and keep your old ones as spares in your tool kit. Did I mention you should get a tool kit?
Chain - $50 to 120 - DIY Check the side to side stretch and make sure the rear wheel is adjusted so the chain has the proper amount of slack.
Brakes - $40 to 120 - DIY for some Excluding disc brakes, drum brakes are not hard to do. Follow your manual or a Haynes guide. While your doing this check the bearings on your wheels. Most often modern sealed bearings are cheap and easy to install.
Oil/Fluids - $12 to 50 - DIY Get that bike warm and drop that ancient oil. Does your bike have a gearbox? How about the oil in those forks?
Fuel Lines/Gas Filter - $10 to 20 - DIY New gas line and an inline gas filter. Once you start running about on that old beast, there will be old gunk stirred up in that tank - use a filter.
And all this, still does not get into making the engine run reliably.