>Calculating weighted differences for each "attibute" on the one hand and somewhat heavy handed in/exclusion from the set the weigthed differences are calculated upon as well as ordering the "heavily recalculated" and the "excluded" set. Calculation done in CoRoutines (ModulaII implementation of parallell execution under DOS, GemDOS, OS/2 and NT-family). As this was a data entry task, such minimal calculation tasks had to run between keypresses and had to implement a multi-level strategy probably best described by analogy to multi-sweep garbage collection strategies in languages like C# or Java. Heavily tailored to the input task and somewhat adjustable if structure and/or quality if data input source was known. Made manual "control" feasible, as previously sometimes cars were not correctly identified, throwing off the total calculation of the price according to the statistical models calculation (done via multiple regression and factorial decomposition from a time series estimate reached via combining "typical" time series) - esp. if not many cars of that special make, model and year were sampled.
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A simple "take a look at Data Mining models and algorithms" might have sufficed :)

Some companies out there have paid hundreds of thousands of dollars for those types of calculations. Some wound up saving money in the long run...and some were just hundreds of thousands of dollars poorer at the end :)

Any company looking to go down the road you described will need to make sure the key business users are prepared to spend some time in a dual-effort sanity check. Even the savvy business users wind up discovering a thing or two in the process of evaluating results.