The reserve is the lowest price a seller will accept. It is normally at or below the low estimate and is not published. If bidding stops under the reserve the lot is withdrawn and the catalogue records it as reserved.
The buyer's premium is charged in bands on the hammer price: a higher rate on the first tranche, a lower rate above it. Build your budget by adding the premium to a hammer price and asking whether you can live with the total, not by working backwards from a total.
