Taking it to a bike shop for a "tune up" is probably a bad idea. It's like giving your fat wallet to them with instructions to empty it. If your bike sat outside for years the labor and parts charges are going to exceed to worth of the bike when you are done fixing it. A better idea would be to buy parts online, go to the various tutorials at Sheldon Brown's or Park Tool websit,e and learn how to do simple repairs yourself. Parts are often cheaper and your labor is free.
https://www.sheldonbrown.com/repairs.html
https://www.parktool.com/blog/repair-help
You may need to buy some tools to get started but a simple tool kit can be had for around $30 and have most of the tools you would need for normal maintenance. It's certainly less costly that an hour of a bike mechanic's time.
Example kit - $30 postpaid
https://www.ebay.com/itm/UNIVERSAL-B...4AAOxyQyJRms~F
