I haven't bought brass in a long time and the OP asked for the current price of brass, so you should probably ignore this post...!
Having said that,....
- it would be pretty silly to pay more than 50% of the price of new brass, so that's sort of an upper bound
- an absolute floor on the price would be its value as scrap. If you can get $2/lb for scrap brass, then each case is worth 5c as scrap.
- for once-fired good commercial brass (e.g. Winchester), I would consider 20c to be the "buy lots and lots" price; 30c and beyond would be pretty uninteresting.
- for military brass, I would want to pay less, due to the extra prep work involved. If I could get 1X fired commercial brass for 20c, military brass would have to be 10c or cheaper in order for the work to be worthwhile.
- having said that, for some people (M14 owners, arise.....!) military brass is more desirable because it is heavier and stronger. For the right market, military 1X fired brass is perhaps worth just as much as commercial 1X fired brass is in another.