I decorated my cage for Halloween last year, however most of the decorations were home-made because I didn’t have the funds to buy decorations. I made a pumpkin carving garland out of toilet paper tubes, cutting the tubes in half and cutting scary faces into them, stringing them together and stuffing them with hay. I also made a castle out of a cardboard box for them, adding castle style windows, adding a stone ledge around the top (I don’t know what it’s called), then I hung a cut-out ghost inside. I also printed out some bats and pumpkins etc on Halloween coloured paper and cut those out and hung them around the cage. Other ideas are coloured or Halloween printed fleece, plastic pumpkins that you could stuff with hay or hide treats in.
I’m not sure I have any pictures, but I do have a youtube video of it. If you search for my channel called Bunny Basics and scroll down to cage tours, there’s a Halloween themed one there. In fact if you just search youtube for Halloween pet cage tour there’s tonnes of ideas as well. 