Best microchip cat door?

I am building my cat an enclosure for his automatic wet feeder to keep my girlfriend's cats out of his food. I was planning on getting some sort of cabinet and then installing a microchip-activated cat door because my cat absolutely refuses to wear a collar. I've seen several microchip-activated doors that range from <$100 to >$300. I don't want to cheap out, but I don't want to spend too much on extraneous features.