Fish Finder advice

Any advice on buying a fish finder for my 3.3m inflatable.

I have a budget of around 100euro, does anyone have recommendations on certain makes etc

Also how can you mount one of these to an inflatable?

there is a portable type that humming bird do comes in a carry case and u could run it off a battery and take pack it up no probs dont know how much doh. we had one for a while on our baot until we lost the tranducer in the prop. black and whit model we had was grand worked good.