The way I describe sleds to folks is like this - Sleds are the attention getters, and full-body decoys are the deal sealers. With sleds, you can pull in scoter and eider from long distance. They show up on the water very well and are quite visible. I would not hunt sea ducks without a set of sleds. Oldsquaw are wary birds, but they usually deke to decoys of their own kind - you could use full bodies or make some Y-boards that are a little bit bigger and will stand out on the water.
I'll have the sled tutorial up on my site today and can work on getting some photos and text of Y-boards up there too.
When I make sleds to sell, I have to charge around $175 for a set of 7 birds. They are labor intensive to paint and assemble. For the cost of materials, you could probably make two sets for around $75 to $100, which would include fir plywood, rough pine for crossboards, glue, paint, screws, filler, etc.
Nate