If it's only truing, it's no big deal. Quite frankly, I think bike shops charge too much for the typical truing. If I'm not mistaken, they may charge $20-$25. I really don't know b/c I've trued my own wheels for at least 15 years now.
And that's what you should be looking to do. Truing a wheel is very easy. Take it to the bike shop a couple of times and have them let you watch. Then go out and read up on how to true a wheel. With not very much practice at all, you'll be keeping your own wheels true in no time.
All that said, make sure you know the difference between an out-of-true wheel and an out-of-round wheel. The former can almost always be put right. The latter usually requires a new wheel or a rebuild. (Out-of-true applies to the wheel's lateral plane. Our-of-round applies to the wheel's vertical plane. The former rubs against your pads. The latter goes bump, bump, bump as you ride.)