Fish finder for ODC 420

[hella356]

Hi! This is a great forum, and led me to purchase the ODC 420, which I had a complete blast using last weekend for the first time. I have been reading a lot of old posts but am having a hard time figuring out what is the best route to go for a fish finder. The Humminbird Fishin' Buddy 120 & 130 look promising but I'm not sure that that's a better route than a more traditional style. I'm trying to keep the total cost to about $200 and will not be using the FF for any other purpose than tubing. Any suggestions?

Thanks!

Mike