If you want to keep the price down, the Phoenix SeaBee is only $99.99 from Tower. In addition to the Great Planes Venus 40 and Sportsman Aviation Excelleron 50 already mentioned, you might look at the plethera of .50-sized pattern ARFs available from World Models at http://www.airborne-models.com The Spot On 50, Aeropet 50, and Groovy 50 are all very reasonably priced.

I'm in the process of building a Thunder Tiger Imagine 50 ARF from Ace Hobby. Interestingly enough, I don't think I've ever seen the imagine offered for less than $180 or so online, but my local Hobbytown ordered one in for me and it was only $144.99. It's not the easiest building ARF, but the wood quality and construction is the best I've ever seen in an ARF.