In your price range, I'd reccommend the Standard Horizon CP180I. It has a 5" color screen, and takes the C-Map Bizer chip. It is equipped with an internal antenna, and can even be hooked up using a cigarette lighter plug (one of my dockmates did this, with good success!)
One of the popular on-line marine dealers currently has it for $395.00; with chip, that's just in the range you mentioned. (I don't want to post a link to another site, but PM me if you like and I'll give you the info
).
Silver Duck