The drivers Wilson uses are pretty typical high end quality units, presumably custom spec, from ScanSpeak, Focal and SB Acoustics. They also do some modifications, which adds to cost. Parts cost is not a big part of the cost of these speakers, or indeed any high end speaker.
To give you some perspective, the woofer is something like a 5" SS Revelator, which you can buy for around $200, and the tweeter I have no idea about but is probably a flat faceplate silk scanspeak unit; the most expensive unit is the old D2905/9700 which is again around $200. Presumably they get some kind of discount, call it 20%, and you're looking at around $640 for drivers. Add another $600 for a very complex crossover using esoteric components and you're looking at maybe $1340 in parts.
The costs for Wilson add up due to all the other stuff though; they pot their crossovers in black epoxy, they probably use nice thick PCBs, their ports are custom machined, the terminals are super high end units. Wilson knows how to create the impression of value to audiophiles.