For a cheap & sturdy cage you can use a regular bookcase, it's really common here in Sweden.
You'd need to waterproof it with something like thick pvc/plastic tablecloth which will need replacing, but it's fun to change it with the seasons.
You may also need to support the back/bottom with some cheap plywood, and many prefer to cut a side out & replace it with plexiglass.
I believe Ikea has the same products all over the world including Norway, but any bookcase with appropriate inner dimensions would work. The Billy bookcase is the most popular one here because of the price & generous measurements, it's about ~15 sq feet. The price differs depending on color.
Ikea Billy Bookcase: Width: 31 1/2" (80cm) Depth: 11" (28cm) Height: 79 1/2" (202cm) Norwegian website: BILLY Bokhylle - bjørkefiner, 80x28x202 cm - IKEA
US website: BILLY Bookcase - white - IKEA
Well, I actually ended up with a commercial cage. At least for now, due to difficulties to find the required materials for a proper C&C cage, and because it was actually of decent size. It was the same cage as Varcoda posted a picture of earlier:
I found it at my local pet store, and it costs 1000 NOK (~170 USD), which was cheap compared to the other big cages I had seen earlier, which was ~250+ USD. Hopefully my two piggies will be satisfied with the new 1,2m cage.