The value of used bulldozers can be determined using the search tool at the Truck Blue Book website. This can be used to search both makes and models by name.
The BuyerZone website can provide more of a broad overview as to what values to expect with its listing of actual prices paid for used bulldozers by some of its users.
The values here cover a range of makes, models and conditions of bulldozer. Prices start at $10,000 for a "550 Case tractor/dozer/crawler" with backhoe and ripper included, and peak at $58,000 for a "1996 CAT D6MXL" with a new undercarriage.