1) No price discussion
2) Never heard that name for a quantity of it before.
3) Mescaline is sometimes extracted from cactus, and sometimes made synthetically. The cactus-derived stuff (which is likely what you were offered) is qualitatively different from the synthetic (in subtle ways, not overwhelming ones, due to other alkaloids present. Some say that synthetic stuff is not authentic, others say that the extract has more sideffects), slightly less exorbitantly expensive. The synthetic is a white powder, extracts could be brown, green, yellow, or white. I have not heard of any mescaline products supplied as a liquid unless someone was doing the extraction themselves and not taking it all the way down to a solid extract.
4) Dose for mescaline is 200-300mg for a common dose; someone saying how many doses it is very well may be shooting for the low end of that (or they may not be), but no honest drug dealer (lol) would sell less than 1g of mescaline as 5 doses. I've been offered extract for that price, and synthetic for significantly more.
5) It's entirely possible that what you would actually receive would be weak, inactive, or some random psychedelic RC that's cheaper to produce instead of mescaline. This is the case with much of the product sold on the black market as mescaline - they can just buy a pile of 2C-whatever and mix it 1:15 with the first white powder that caught their eye in the spice cabinet, and sell it at an obscene margin.
