I have been using the same brand Ray has shown in his post.
a few months ago, I picked up an 80L / 1Kg package for $39 + $6 shipping through eBay. Being as I am remote,
shipping is always a major consideration in the final price.
If they do not ship by USPS the cost is usually too high.
Right now, on eBay that package is going for $30 to $50 + shipping.