Suggest one of the Cheshire Dinghy and Dive Baggy Trousers but there were only a handfull made. You might also consider a design-8 or a Final Chapter in plastic.
Peter,
There are almost no single-bottom 12s that are worth more than that. The best bet is a Design 8, but that is such a consensus view that they are very hard to find on the market and go pretty quickly. If you can get a plastic hull wooden topped Waller Chapter then it is a great buy for an open water venue, they are a bit tough to sail in light weather with lots of roll-tacking.
Looking at the current on-line list there are none of the above for sale, and if you are set on plastic then it has to be 3374 or 3404, both plastic hulls with wooden tops. Either will work for the weight and the venue, obviously one is twice the price of the other and there are reasons for that.
If there are other boats that you want more thoughts on, or want more detail off-line, then email me at antonygifford@aol.com and I can find you a view if it is not a boat that I know.
Perhaps somebody who reads this will know of an un-loved D8 sitting somewhere.
Antony
N3484