Portable bottle warmer

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I have 6.5 week old twin boys and a 3yo daughter and we are fairly busy and I’m looking for a good portable bottle warmer that doesn’t have to be plugged in. Preferably one that doesn’t need water out an outlet. Just one I can put the bottle on and warm also one that’s not super expensive (less than $100). I’m thinking of something like the product below but cheaper. Thanks