I dont think you have to be real close to the fish.I have not relly tested the range, all I do is just drop it down and then kinda drag it around untill I see fish.
Its very easy and fun.

They sell for anywhere from around 200.00 up with the average being around 500.00
Of course you can get all kind of extras if you want like longer cord,ect.
Also you can look at the different brands and some are cheaper then others.

Shaunpm