I agree with pretty much everything ForceFlow said.
I think the most cost you will have will be in the electrical.
I did my electrical last year, I went from 150amp to 200 amp on my house which needed done and then had them go ahead and run it to the garage. They installed a sub panel in the garage and it is now 220V. So I can run my heater in the winter and ac in the summer. As well as compressor, sander, radio!
I would say look into the cost, do some measuring and see how much material you will need.
Have a electrician come by and shoot you a bid, most will do free bids.
Is it worth it, Depends on if the wife will make you sleep out there when you buy your first NIB!