BigDavie head I'm not sure, but for the 80k leggings, I would say 900k plus. There's what, like 3 full sets? I believe that's the price for those, or so I've heard.
I'm sure there's people out there who would pay well over 100k for a Bigdavie head, you just have to find someone willing. As for the 80k Member Leggings, there's not a solid price you can put on them because there are so little of them. You could easily find buyers at anything above 500k though I'd say! The higher the price you put on it, the lower the chance of finding a buyer - but you may be able to find some that would pay a lot higher.