As suggested if it aint broke then don't tune it up is like saying "
if I have checks in my check book then I can still write checks".

Firstly, a Tune-up is really a very basic adjustment to the cables, crankset, some lube adjust the brakes.
THEY WILL NOT FIX THINGS beyond that (usually).
Based on location a simpleor basic tune-up is about $40-60. Mostly covering what I stated, maybe slight true to one wheel, maybe.

If you maintain the bike, clean, lube, wash it down correctly the chain, cassette, cassette, wheels, pedals, cables will last a long time without any replacement of parts.
Okay, how long is that?
Figure 5,000 miles plus before you bring it in. This is not a written rule but a general rule.
I ride 5-7000 mile on one bike yearly and usually swap the cassette and chain yearly, plus all cables and brake pads. I ride 12 months a year in NYC, not in snow, but wet conditions don't always keep me off the bike.

okay, you rather pay for the fixes, thats okay. But learn how to keep it on the road and you will live longer. Its a machine that you sit on. Hate to have your chain gunked up and break or wheel go flat for lack of air.

remember, the only thing between you and the ground is the bike.

Good luck

robert