Euro car parts advertise in their online shop Triple QX Purple Antifreeze Coolant Long Life G13 Fully Concentrated 5 Litre for £18.99, which is reduced from £23.94. I bought this on Ebay for £14.24 using Click'n'Collect.
So if you are buying from Euro car parts, be sure to check on Ebay first. They(Euro) operate a price promise which you can view on the online shop. I think just going in and buying over the counter may prove to be expensive. ;)