I don't usually expect much in the way of gardening bargains in the January sales, but Homebase this year have come up trumps - 60 litres of peat free compost substantially reduced as you can see from the picture. January would normally be one of the worst times to buy compost too - the bags on sale have usually been left outside for months and consequently have had a lot of their nutrients leached out and aren't a good buy. However, the bag I bought a few days ago had been kept inside in the stock area, was for sale inside the shop and was therefore OK. Just as well as I still have a few tulip bulbs left to pot up as I ran out of compost just before Christmas.
At other times of the year, you may pick up similar bargains. Stores often have a cheap deal going on 3 bags of compost and I use the empty bags as a weed suppressing cover on my allotment. I have 10 compost bins on the go, so you'd think I'd never have to buy any wouldn't you? But I seem to have a garden and allotment that obeys the law - the more compost you have, the more uses you can find for it, so the occasional top up is needed. Also keep an eye open for broken packets, not just of compost. I found an enormous bag of purple slate chippings for £1 a couple of years ago which I've been using as a decorative mulch for my pots ever since.
The pictured bag turned out to be even more of a bargain - the recent VAT reduction was taken off when I took it to the till, so the final bill came to £3.40 :)