RE buying cheap last day of the show, you will be the LAST in line to get a deal on anything. If the item is getting sold, most are NOT, first dibs will go to reps, dealers, other vendors, somebody that knows someone in one of those groups, etc, before you. General rule, the bigger and heavier it is, the smaller the manufacturer is, and bigger the crazy price is, the bigger the possible discount.
Only a few very odd drivers make less distortion as output increases, and those that do its generally only at very low levels then the normal rising distortion. With a horn the efficiency is increased so you get to listen to the driver at its 1 watt distortion level instead of 50 watt distortion level.
Some of the best horn drivers have 2" diaphragms, that means 2" throat on the horn and generally a big horn. Bigger horn means more efficiency and mouth size related to lower frequency cutoff point.