My boats are all nitro powered but we have several people that do run them in the R/C Unlimiteds electric division. Bill Brandt would be someone you can contact who has first hand experience.
The Turnigy and Typhoon motors are more budget oriented options but suitable and able performers none the less. All these mentioned motors are 39mm diameter cans and around 4 inches long.
The Scorpion/Hyperion 4035-800kv is a proven performer too and cheap, however that wind/rpm is no longer in production and a little difficult to find.