Lots of questions....
Here is what I currently use:
Garmin GPS 12
Axim Basic w/128MB SD card.
Mapopolis (This will be the most recommended software hands down.)
w/Platinum+ GPS maps(But the Navigator maps have voice directions for handsfree.)
Garmin PC Serial Cable
Dell Serial Cable
Radio Shack 9 Pin Male/Female Null modem adapter & Male/Male gender changer.
I don't know if anyone has had success with a E-trex PC cable and an E-trex, but others like myself have had success with other models. Magellan users I believe have also had success.
http://www.gps4fun.com is a good place for GPS receivers, accessories, and prices.
Maps: The Mapopolis map subscriptions give you access to all the states and the county maps in the state. In my case the Mapopolis Platinum+ GPS($44.95) maps for the state of Georgia is around 20MB for all the counties.(It is the same for Navigator maps $99.95.)
Navigation Software: Mapopolis the program is only 244k in size and is free. The maps are what cost. The closest zoom you can get is 100 Feet. Farthest zoom out is 1000 miles.
Storage card: SD is smaller and comes in 64/128/256/512MB's. Average price for a 256MB is around $80. Compact Flash is a bit cheaper, but a tad bulkier. I choose SD so I have the Compact Flash slot free for CF devices like a Wireless network card.
Topographic Navigation software: Delorme makes Xmap Hand Held($40'ish) and Topo maps($90'ish). Haven't used it at all so I don't know how well it works.
Hope that at least gives you some idea of what's out there.