I just ordered silnylon from Noah Lamport (noahlamport.com). They don't have it listed on their website, so you have to call them for it, and to find out what colors they currently have available. When I ordered, it was $3 a yard, but you need to order at least 10 yards of a color, and there's a cutting fee of $5.
I haven't found out how much the shipping is going to cost me, but I asked if they could fold it, rather than roll it to save on the shipping cost.
With the shipping cost, and cutting fee, I expect/hope it to cost $4 or less per yard.