Just stumbled onto a stainless steel box for sale for $10 online!
My cubic inches to ml says it's around 850, but that's including the domed lid, and rather approximate, as it has rounded corners. Good for sandwiches and bulky fruit and salads, probably. But cheap! They also have a 12oz stainless steel bottle with nipple cap for babies, but it says a sport cap is available, I guess on request. Also $10.
My Dearest Friend, If You Don't Mind, I'd Like To Join You By Your Side, So We Can Gaze Into The Stars, And Sit Together, Now And Forever, For It's As Plain As Anyone Can See, We're Simply Meant To Be.