Here are a couple of up dates to my previous points.
First, if you click on the attached url you should see Sitex trnsducers starting at $9.99
web page
Second, i did check out the Garmin 3005. My opinion is that it is very nice & state of the art, and that you are paying a premium for its various add on capabilities (such as a sounder for another $250, satellite weather at $500+ and other misc. bells and whistles).
It uses the same bluechart maps as my Garmin 178C.
Here is my biased take. If you are just looking for a solid color GPS w/FF capabilities, I would take the Garmin 178C. It will be several hundred dollars cheaper. however, if you want the capability to support satellite weather connectivity and the like, than maybe this is a good unit to go with.
Just my 2 cents.