I've seen people try to sell them for several hundred, but I've also seen them go as low as $20, or even for free just to clear up closet space. Most of the 6CD's I've seen go for around $50-75.
I'd been thinking about taking my stereo apart and sticking part of it under the dash somewhere to try to make my trip computer work again. I guess this tells me I'm not risking much by trying...