Vinyl sheeting and sealer recommendation needed

Can someone provide me with a recommendation or referral?

I’m looking for a good source of vinyl sheeting for a prototype - the kind that they use for making hot and cold packs, so it must hold up at temperatures near and slightly above 130F without seals being compromised. I’m also looking for an inexpensive sealer for this vinyl. I will need to make several small to mid-sized bags with it, probably nothing larger than 12" per side.