If you're shopping for a used Prius, expect to pay $4,000 more for one with the carpool sticker. That's what Chris Woodyard of USA Today found out when he asked Kelley Blue Book to sample prices. Carpool stickers allow the vehicle to cruise the HOV lanes in California even if there is only one person in the vehicle. The state gave out only 85,000 stickers, and the stickers stay with the vehicle, not the vehicle owner should he purchase a new Prius or another qualified vehicle. KBB's sample showed that a used Prius with the sticker will draw about $4,000 more in the sale price than a similar model. It all depends on what your time is worth when sitting in traffic.