The Nacra 5.5 (Uni or SL) would be good and should easily be with-in your 5K budget. I used to have one, with a spinnaker, and single handed all the time. The biggest disadvantage compared to a newer boat, such as the F16's, is the weight. It can be a problem righting the boat single handed, and is a little more difficult to move around the beach. I know of one for sale in Texas if your interested.

My Nacra pages:
go to http://taipanic.us/ and click on the Nacra Pages link on the second line.