You can buy a Lowrance unit for under $500 that is very nice. Here are some features (copied from a web site)
- 5" diag. 256-color SolarMAX TFT display for maximum visibility and widest viewing angles even in bright sunlight
- 480 x 480 pixel resolution for superb sonar target detail/separation and exceptional chart definition
- Advanced fluorescent cold-cathode screen and keypad backlighting
- 5-pin Ethernet expansion port compatible for radar, video and satellite radio
If you order now, you get a free chart for the US on a chip.
I like Garmin units, but I think they are overpriced. For more money, the Garmin 440 has a smaller screen with less resolution:
Ultra-bright 4" diagonal QVGA display, 320 x 240 pixels - over 800 nits of brightness