I have a Lowrance 3500c with Navionics Gold chip and am very happy with it. There are a lot of NMEA networking options that you can add on like the fluid level and fuel flow meters. Mine now tells me gph and mpg as well as fuel level. Some other models (5300c) are on Ebay (new) for $435.
http://cgi.ebay.com/ebaymotors/LOWRA...spagenameZWDVW