How about finding someone with a big enough freezer (we used a local company) who will freeze 100mm water in the bottom of a plastic storage container (those ones that stack in or on each other depending on which way round). Freeze two ends of some string in the bottom. You now have an ice sled! Take it to the local park with some carpet or towels to sit on and slide down grass slopes. We got 4 made for about $40 and they lasted hours until the kids ( and us) were worn out.