Here is the lowest cost we found. For 10,000 18X30 polypropylene bags, $3104, or 31 cents per bag, including shipping to the island we live on. Donald Davis Bags in Spartanburg, South Carolina gave us the lowest price with shipping. This, of course, does not include duty and VAT that we have to pay on our island.
Our house will take 3600 bags, making our walls cost around $1116. Not bad.
The rest of the bags will build retaining walls and a garage.