I haven't found a 500 dollar boat like the fellow at the yard sale!  Wow, what a deal.  That said, I am going to get me a tube float and get out in the lake near my house.  I had been thinking that I'd like to have a depth finder to see what is underneath me.

I did a google search and saw several portables on ebay from 40 to 60 bucks.  Does anyone have any experience with these things?  Do you think it might be practical with a tube?  I also have use my neighbors jon boat so a portable might be the ticket.

Are the portables, so cheap, any good?

Portables are OK. But you don't need to use a portable. You can use any fishfinder you want to buy. All you need is a 12 volt power source and get a little creative. I use rechargeable AA batteries to operate my fishfinder. I went to radio shack and bought a battery holder for 8 - AA batteries (cost $2.oo) and to walmart for a waterproof container (cost $8.oo). This will operate my fishfinder for 3 days.