A well made 10.5 x 10.5 silnylon tarp for 80 bucks?
Heck, I'd buy one for myself!
Not sure if you'd sell 'em for Non-Scout applications though.
I have been involved in Scouting in the past but not anymore.
I do drag my numerous nephews out into the woods though, and almost always use poly tarp shelters when I do. I'd love something lighter and would also use a tarp like that for other trips as well.
As far as other tarp shelter types, the Ray Way type tarp with "beaks" might work well. I'd not bother with a sewn in floor. It would take much abuse ( especially in a large shelter where Scouts will enter with shoes on ) and be difficult to clean.
I prefer separate ground cloths, and in a big shelter several ground cloths could be used to cover the floor, giving every Scout something to carry to contribute to the shelter ( and every Scout would have at least something in their pack that could be used as shelter in a pinch ).
In the past I've made the Mini Bull Designs Hasty Hooch out of a poly tarp and two of my nephews used it on a week long trip. The glued seams started to come apart, but it did work well and the design certainly is sound.
It could easily be scaled up quite large, and might be a good idea for a patrol shelter. You could sew in a "sod cloth" around the perimeter, mesh door flaps to keep out insects, and use separate ground cloths.
My favorite ground cloth has always been the "Sportsman's Blanket" or military "casualty blanket" or "Coghlan's thermal blanket". It goes by many names and is a bit heavy at 12 ounces but I sure don't mind a Scout or nephew having one in their pack, especially if they have nothing else for shelter or rain gear packed.