Even though I was in charge of applying the Tordon I don't remember any particulars, other than the price, which I specifically asked about. I thought the forester had said it was expensive, but I thought $15/quart was fairly reasonable, considering how far it went. We used it straight out of the bottle and it was a very visible green/blue, so it was obvious what had been treated. Dad said it was pretty nasty stuff, so I used rubber gloves while applying.
Girdling is cutting a ring around the tree, maybe an inch or two deep, about waist high (though I think that's just for convenience). This outer ring of the tree is where the sap is carried and will kill the tree. Not as fast as cutting it down obviously, but very effective, and much safer as far as the bigger trees are concerned. You don't have to worry about a tree falling on you. We then went around the girdle and covered it with the Tordon.
If the forester mentioned it, and he probably did, I have since forgotten.
I do recall him saying that there was no way you could get them all in one pass. They are hard to kill and you will have to keep at it for several years as you find more that you missed or have popped up since your last attempt.
In Indiana you can set up a walk through with a forester at no direct charge to you (obviously your tax money is paying his salary). It was very interesting and well worth the time (it took maybe 2-3 hours for our 30 acre woods).