Seriously, it will be as precise as any high-end stand. We'll take an inexpensive but solid Performance Spin Doctor truing stand and add threaded indicators to make it much more effective - faster to use, more durable, and light-years more precise - for less than $7.
Step 1: Our base: the Performance house brand Spin Doctor II truing stand
This guy is always "on sale" at performancebike.com. As I write this it is $49.99, but I have seen it as low as $39.99 occasionally.
In addition, there are lots of ways to get it cheaper. Personally, I think I got it for $49.99 - 20% off offer - 10% Team performance + free shipping offer, so about $36, which is why I say that this project can be done for well under fifty bucks.
First of all, Performance basically always has at least a 10% discount code around. Check out bikeforums.net in the coupon forum - you'll often be able to get or ask for the latest one. Also, Performance regularly offers free shipping, so you can get on their e-mail list and keep an eye out for that and other offers. If you happen to live near a Performance you can also have it shipped to the store for free. You will have to pay sales tax, but if you live near a store you will probably have to pay tax on an internet order to your house, too. Finally, if you buy bike stuff regularly, it may worth it to pay to be a Team Performance member, where you get 10% back in points to use towards other stuff, plus faster shipping.
I am not connected to Performance Bike in any way. I just happened to buy this particular stand for myself, and this instructable uses it as an example for modification. You may find other inexpensive stands on the market and be able to do similar modifications. I personally haven't seen one that is of this quality for less, however.
Clearly if you're handy you could try to make a stand from wood, metal, plastic, whatever, and add threaded bolts in a similar fashion.
There are two reasons this will be tough, however, and may make buying a pre-made stand worthwhile:
1. Different wheels have different axle lengths, and your stand will need to adjust for those differences and still remain rock-solid.
2. Most wheels with quick-release hubs are actually not fully tightened to the bearings until the quick-release is clamped down. That is, if the quick release is not tightly clamped onto the wheel hub, the wheel actually has a little extra play in it, and this will affect how true you can make your wheel. So your homemade truing stand will have to allow for this solid clamping and still remain rock-solid. You can't just rest the wheel in some slots and go at it. Well, you can, but don't expect to be able to get really tight tolerances.
(I am using a pic grabbed from the Performance website without their permission. I suppose this instructable may drive some traffic their way however, so I doubt they'll mind.)