If this morning's Swedish cardboard playhouses gave you a nosebleed with their 370 Kroner pricetag (approx US$3,221,145.22), you can always make one yourself, with a set of plans like these:
It is easiest to start with a large cardboard box such as a refrigerator or other large appliance. I called my local appliance store and had them save me a box. I told them I was making a cardboard playhouse and they were more than happy to set one aside. If you can't find one large enough you can certainly construct one out of smaller boxes, it will just take more time to piece it together.