man,at that price you need to find a good used Tesoro "tiger shark" or "sand shark".stay away from fisher water detectors they are all Chinese made.water machines are very expensive and you pay the big bucks to work on them.Tesoro has good warranties on any thing they sell new.The top two best warranties and less expensive on maintenance are Tesoro and whites.
IF you just want to hunt in knee deep water any land detector with a water-proof coil will work.Tesoros are really good on gold the "COMPADRE "IS REALLY NICE IF YOU ARE JUST STARTING OUT!Its very cheap and has a very good discriminator and has a 8" donut coil .I have had one for $160 and has a LIFE TIME WARRANTY.It has one knob very accurate detector it does it all, 6''----8" average depth,auto. ground balance.IF you want a deeper one the "CIBOLA" will do 12"deep but runs around $ 340.Hope this has help.---james