1) No I don't think qt will count toward the budget cost. While be it I think I could setup a qt for less then a 100, I would rather not have anyone taking unnecessary risks here.
2) Yep that works fine. If you bought it used, then you bought it used. Charge what you pay for it. If however you got it for free, then you should charge your self a reasonable used price for it.
3) yes shipping and taxes are ultimately part of the purchase price, so if you paid it, then you should charge yourself for it.
4) Sale prices are fine too. Again, if that's what you paid for it, then that is what you should charge yourself for it.