lpkfusa.com has some awesome products thats for sure, for a slightly cheaper alternative I have found www.thinktink.com They have soldermask ($300 for 40ft) as well as a through hole compound for $70 and you just need a simple copper electroplating setup (
http://www.thinktink.com/stack/volumes/volvi/condink.htm)Pulsonix fab-in-a-box even ordered from them is pretty reasonably priced. $80 for the laminator and $80 for the starter kit that has two 10-packs of paper, green and white toner foil, single and double sided A4 size pieces of FR4. $160 was a no brainer as I ordered one board from a fab house and the damn thing didn't work and bam $75 out the window. At least now I can test it many times before I send it away. I have been using it every few days for 6 months and am still on the first pack of paper!
If you want the cheapest way do what other suggest and ebay the laminator and just get a package of the paper for $18 off digi-key.com I don't even bother with the green or white foils (not solder mask they melt under any heat) But you can get 6mil traces with 8mil isolation time and time again no worries.
So back to the original topic of dry film solder mask. I have heard of liquid solder mask, where can you get it? I don't mind having to do a UV mask as I already have the equipment and Its the same setup for the dry type I imagine.