the BHO mirror test is a good one, also colibree is good, I would use no less than 3x refined(5 and 7 times refined are available), and if your looking just to try then yeah its costly, as far as how much your gonna use depends a big deal on your extractor, the bud or shake, but allot on the extractor. I recommend okeif BHO extractors since their cheep and very good. and if your gonna make bho it is cheaper to buy your butane in bulk so you pay more like 3 or 4 dollars a can and not 12-15 a can, but you have to buy allot like 300 bucks worth. now if your just trying some bho, remember even a test batch your gonna need like 5 grams or more of raw buds to get like 5 or 6 hits, maybe more maybe less. and your also gonna need a special design of extractor, those okeif ones dont work properly if you just use a little bit, the butane just goes around the bud, so if you wanna try it is easier to get some at a cannabis club, or your gonna spend allot.

remember the more refined the more pure the product, butane can have all kinds of impurities in it so a well refined butane is important. as well as knowing what your doing, the evap process is very improtant.