I can almost guarantee that you wont find a new color fish finder for under 100 but craigslist might have one. I personally dont think color matters too much. A good grayline fish finder will do the  same job as a color one. plus you can get one with a lot more features for less.

With a good color fish finder you can tell if the grass on the bottom is dead or alive. You can pick a fish out of a brush pile. And with enough experiance you can tell the type of fish...... I will never go back to gray scale fish finders.

As for you question. It will be hard to find a good one under 350. Here is the cheepest one I could find. It's 220.

http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_10200012_250003001_250000000_250003000_250-3-1

The Eagle Fish easy 350 is also $220.  That and the Hummingbird are the cheapest I've seen.

http://www.basspro.com/webapp/wcs/stores/servlet/Product_10151_-1_10001_10200082_250003001_250000000_250003000_250-3-1

Be careful with choosing a cheap color unit. Most of the cheap ones have a terribly low pixel count. I would stay above 320 x 320  pixels.