Foxpilot,
To tighten the spoke, find a fixed starting point like a rim lock or valve stem. Tighter every third spoke no more than a quarter turn or so. After three times aroung your starting point, you have tightened them all.
Now as far as which way to tighten the spokes, think of it this way. It is ALWAYS CLOCKWISE when you are looking down from the top of the spoke (inside the rim), imagine the tire off the rim and you are looking from inside the rim.
If the spoke is on top, it will LOOK like you have to turn it counter-clockwise but think FROM INSIDE the tire, it's CLOCKWISE.
As far as how much it would cost, Most shops (in my opinion) don't know what they are doing when it comes to truing. There are some specialty shops that only do wheels and wheel building. They charge around $25.00 to True the wheel.
http://www.tcrwheellacing.com/index.html
I have never used these people because I build my own wheels and I'm on the East Coast.
Hope this helps.
Jeff