Rob. make one yourself !!! Something like the MFA piranha is nice and easy to make, has full instructions and is fairly fast , foolproof and very tough. Its nothing particularly special, but on the other hand, you will have the satisfaction of having made it yourself.
Dont forget that your air radio will not be legal to use in a boat (27M 40M or 2.4G required) so you may have to buy an r/c set, but a 27m kit is fairly cheap .
£45 MFA boat, £10 motor,£15 battery £20 ESC £35 ish radio…glue .as a guide verses buying something secondhand. It depends of course if buying secondhand…sorry “pre-owned” how fully equipped the purchase is and how much work may be required to get it running well for the odd occaisional zoom.
If that is any help?
Ashley