Brandon- Aquamend isn't much, although I can't quote you a price.
I also use aquamend for rock. I've used it to do some funky stacking in our nano, to support a little shelf in my 90, and to cantilever a plate coral in our 92.
Two things to know in using it:
1) It doesn't stick to rock very easily and takes a while to cure, so you have to really gum it on the rocks your attaching and devise a way to hold it in place for a while so that it cures all the way. A lot of times I use superglue gel on the faces of the rock with aquamend in the middle. This assures adhesion to the rock surfaces and because the superglue cures quickly, you can usually get the rocks to stabilize a little faster (which could be really important if you're trying to stack liverock in a dry tank without experiencing much die-off).
2) Aquamend can cause your skimmer to overflow, so turn it off/down and/or monitor very closely. This effect is obviously worse the more aquamend you use at a time.