I buy what I find cheapest. I haven't bought any off of the internet because when I want them I want them now. I know I could save a few bucks by planning ahead that's not my nature on these type of things.
I've used off brand rolls and never had a problem with them. They've sealed and kept the seal as long as was needed. Please don't ask what brands they were because I couldn't tell you.
As to where I got them. Wally world once had some but now I only see the Food Saver rolls there. K- Mart was another place along with the local hardware store. They sell everything.
I say go for it. How tough to they need to be for life in the freezer.