you ca pick up a decent 5.4 searider for around 5 to 6K with something like a 90 hp on it this will amply fill your requirements you can then beat the stuffing out of it for a season or two and get most of your money back!
seariders go down to 4 mtrs My favourite rib ever was my 4.7 mtr searider with a 70 yummiha on the back.
Other boats worth a look secondhand would be Humber, ribcraft, and definitely think about a Flatacraft if you find one they were strongly built boats and worth a go.
Here it comes again, I don't stand a chance
Soul possession, Got me in a trance
Pullin' me back to you - Deja Voodoo