£10 saving challenges are a great saver. Bit more pricey to save but still a great way to save.
These once filled can save you £800
They are made from 160gsm card & laminated in gloss lamination so can be reused again and again.
When It comes to using use a sharpie to mark off and when it comes to needing to clean it off. All you need is a cloth/cotton wool & 100% acetone or antibacterial gel to clean it off to begin the process all over again.