Hi Got, I'm glad to hear that you're moving into mold making. Aside from skulls, you'll be amazed at the things you can copy. I'm afraid that you have a few misconceptions about the mold making process though.
The first problem seems to indeed be that you're applying the latex much too thickly. Apply thin layers, and don't wait until the layers are completely dry, they should still be "tacky" to the touch. After the first two thin layers of latex which are used to pick up the detail from the original, you should be using cheesecloth with latex for every other layer. Also, heat (in the form of the hair drier) is a prime killer of latex, it's use at any point around latex should be avoided.
A 16oz. container of mold making latex that I purchase from Michael's craft stores for about $7 using their 50% off coupons, is more than enough to make one heavy duty skull mold. $40 estimate for a skull mold is way out of line. Where have you been getting yours?
As far as worrying about tearing the mold when you remove it by making it thick, you're actually getting into a different problem. A thick one piece latex mold will be very difficult to get off at all. I usually cut a slit up the back of my skull molds to make removal easy, while still maintaining the thickness necessary to not have to use a mother mold. It leaves a small seem line that I have to trim off of each copy, but it's well worth it as far as easy removal goes.
Here are some small how tos on mold making that might help>>>>>>>>>>
If you're going into making foam skulls with 2 part foam, here is what my latex skull molds look like for that particular process.>>>>>>>>>
Latex skull mold before removal from original>>>>>>>>
Latex skull mold after removal from original, with air holes, and pouring hole cut out>>>>>>>>>>
Skull mold taped back together with foam poured in, before copy is removed.>