The scale in pepakura is in mm. CM to MM = add a 0, 20 cm = 200mm. My guess is that his scales are for the height of the part. For a full MKVI you will need more than a gallon of resin. There is a great thread somewhere about the project triangle you should read. There are three options for your suit. Fast, Nice, or Cheap. You can only pick two. If you want a good looking suit you can either do it fast and expensive, if you want it cheap it is going to take you a long time. In general, if you want a good looking suit it is going to cost you a fair bit. Expect to spend several hundred dollars, and that is really on the low side of things. If you just want to pep, harden and paint, without smoothing or adding detail, then you can do it a lot cheaper. If not, well, its just not a cheap hobby at all. Just the nature of the beast.