Real Techniques Cheek and Lip set £7.99 at Superdrug, plus 20% student discount at the present time (if eligible with NUS/unidays ID)
Set has an exclusive cheek brush, a duo-fibre contour brush and a retractable lip brush.
RRP for these 3 brush sets is around the £20 mark, and cheapest I could find elsewhere online is around £11/12, including on ebay (but at least at Superdrug you know they're genuine!)
Sadly, they are sold out on Superdrug website, but they had lots of these in all local stores near me! They were labelled as full price on the shelf but scanned as £7.99 at the till in all stores, and there were extra packs hiding behind the sculpting set which looks very similar!.
Might be worth requesting a stock notification in case they restock the website too