I've had good experiences buying from these two vendors and thought I'd pass it on.
I recently bought off-brand rolls for the Foodsaver and they work great. They are commercial versions that are used by professionals. I've frozen stuff in them and microwaved - and they seem to work every bit as good as the Foodsaver brand material. The only drawback is that they are sold in 50 foot rools, so they don't fit the Foodsaver cutter directly, but they can be easily re-rolled into smaller rolls. These sell for $29.75 for one each 8" and 11" roll, each 50' long. Plus $8.10 for shipping, that works out to 38 cents per foot. About as low as you can get (or so I thought).
The seller's name on eBay is: elrodharris.
He has a shop called All Vac Sealer and Butcher Supply.
But as I was looking around on eBay, I found that the guy I had used previously for the regular Foodsaver brand rolls had dropped his prices. He sells any six rolls for $29.99 same as before, but he's dropped his shipping to $9.99, which brings the cost to about 34 cents per foot. That's definitely as low as I've seen.
This seller's name is: foodsaver king.
His store is called FOODSAVER STORE.
Compare to prices through Amazon (cheapest deal is about 50 cents/ft) or direct from Foodsaver - 12 rolls of either with free shipping (but with sales tax) = 48 cents/ft for MA. I don't know the prices at Costco, but I do know that they sell the 6-roll pack (4@11" + 2@8"). Next time I'm there, I'll check out the prices.