This Halloween I'm going as an aperture scientist and I needed a companion cube for my costume. Unfortunately valve sold out of their plush cubes long long ago and I needed a cheaper alternative and fast. So I decided to make my own companion cube real quick, and it took me under 10 dollars to make.
A styrofoam cube
Any size will work but if you get one bigger than I used (5x5x5") you will need to get extra felt sheets and it will get more annoying to carry around.
3 sheets of dark gray craft felt like the ones shown here
3 sheets of white or light gray craft felt
1 sheet of pink craft felt
Glue ( regular craft glue or Tacky glue works fine. I like the quick dry Tacky glue)
You can get all of this at a chain craft store like Micheal's or A.C. Moore. The cube should cost 2-4 dollars and the Felt will cost about 30 cents a sheet. The glue cost me about $1.50. You could use colored paper instead of felt, but I found buying all the different colors of paper was more expensive than getting the individual felt sheets.
First cut the darker gray felt so it covers each of the 6 sides of the cube. If you used a 5x5x5" cube you just need to cut out 6 5x5" squares. Glue them on to the sides of the cube and make sure all the foam is covered. I'd let it dry before gluing the next pieces on.
Next cut the shape out of the light gray/white felt pictured below. You will need 8 identical pieces, one for each of the corners. Be generous with the glue as the felt tends to soak a lot of it up.
Wrap this around the three sides of the corner like so:
Finally, cut 6 circles out of the white/light grey so that they fit in the center in each side. Glue them on, then cut 6 hearts out of the pink and put them in the middle of each circle facing different directions.
I slapped mine together in about half an hour before I had to catch a train down to the city for a party so they assemble pretty quick. As for the rest of my costume I got a plain lab coat/ Iron-on fabric printer paper and just made some aperture laboratories logo transfers to put on the coat. It's not a picture perfect replica of the in game cube, but it works well as a costume prop. If you got a bigger cube you could probably make it more detailed. read