Too much in my opinion but it's probably relative to the wheel. On a crazy expensive wheel that you don't dare mess up, I could see it. For an entry level wheel costing $30-$40 there likely isn't much point in spending $29 to true it.

Also I wonder if "true" means to just tweak the spokes until the rim is straight, or to re-tension everything. If the shop is going to correctly tension all of the spokes to a precisely correct range, and the rim would still be round and true, then maybe it would be worth $29 even on a cheap wheel.