Hullo and welcome
In my humble opinion the handheld fishfinders are not worth the hassle, I have fitted small fixed-sounders to SIBs and it seems to pay off in ease of use.
Garmin do two small black and white screen models that work well, both are well under a 100 quid including transducer (the bit you get wet).
If you want to spend all your budget then go colour for about 150.
I know very little about fishing, but when I go out with people who do they seem to be less interested in the little fish symbol than in spotting an interesting bottom feature. Yes Wilk, I am now going to say crevice.