I think I have a fair idea of how to pull that part off...getting my measurements exactly right, however, would be absolutely critical to get the effect to work. I expect in order to pull it off, I'd have to have not just a mould of my head, but also of the neck and shoulders area to build on everything. What I would guess I'd have to do would be sculpt the neck ridges and then layer on the initial coats of latex--and then once everything was dry, take it off the sculpture and fill that area in somewhat to give it enough strength to hold up to having the neckline of my shirt/dress on it without giving way.
The wig, in the case of the design I have in mind, actually appears to be one of the less costly parts of the costume considering there would be no complex styles involved...all I'd have to do is get a simple straight-haired wig and then weave the braids into it myself. I think I already have beads on hand that I could use (and if I don't, I could get hold of something cheap that would work). The clothes probably wouldn't be awful if I can get some things at a consignment shop on the cheap to experiment on and destroy if necessary.
Figuring out how to do the rest on discount (but still get something fairly authentic-looking)...that's going to be tricky! Realistically, it now seems like I'll have to build this up over a few years at least, to avoid breaking my budget at any given time.