Pricing by Threshold

Looking to setup a pricing structure such that the same price is charged for multiple units with threshold ceilings to chance the cost.  For example any number of widgets purchased between 1-25 is $15.  (Not $15 each, if you buy 1 it costs you $15.  If you buy 25 it costs you $15).  The whole structure is:
1-25 for $15
26-99 for $25
100-199 for $50
200-299 for $75
300+ for $100

I tried to setup a quantity pricing schedule such that item 1 had a 0% discount, item 2 had a 100% discount, item 26 had a 0% discount, item 27 had a 100% discount etc. with and without selecting 'Use Marginal Rates.'  When I try to use the quantity schedule on an item, it changes the prices I set to increments of the lower price (makes me think quantity pricing does something different than I expected).  Then when I purchase an item with this model, it continues to calculate a cost / unit using the unit costs set on the