Just seen the reduced section in my standard size local tesco and they had the big (20kg I think) bags of their own playsand for 71p. There was an SEL with the price.
I checked the receipt and it had also taken 71p off as they were on 3 for 2 on kids toys/books.
I appreciate this will only be stores with excess summer stock so not all stores but worth keeping an eye out for.
It's also good for sweeping into block paving too!