I was thinking of mini as well. I was thinking if you have about 20, you can buy a big bin in a pound shop or wilkinsons to keep them in and wash 10 at a time or so. A 60 degree wash with an AAA machine uses about 1.5kw so about 12p electric + say 2p for water (don't know how much 40 litres costs) - just an idea. Just like doing babies nappies
But they should last a long time.