Yes, that seems like a typical and even fair price for parts and labor, but it's such a fundamental task people that are at all budget conscious should do it themselves.

$18 should buy you a patch kit and 1 or 2 tubes. Stay away from 'glueless' patch kits, they are just stickers, they will get you home, but not last forever. You want a proper patch kit with vulcanizing glue, which chemically bonds the patch to the tube to seal the puncture. Park VP-1 is good, many people speak very highly also of Rema patch kits.

I highly recommend you get a pair of Pedro's tire levers, they're just the best, and only about $5, surprisingly cheap among the landscape of high-priced specialty bike products.

And then for on-the-road repairs you'll need a portable pump to bring on your bike if you don't already have one, that would take you out of the $18 range though.