S.
I just bought 2 of the metal thermos sippys with straws at Target. They seem to work great. They are normally $15.99 but I got them on clearance for $8. I don't think all characters are on clearance, but if you're not too picky you could probably still find them. They were in the section with the backpacks. Hopefully they still have them.
Good luck!
S.