Witch Hazel without a fancy name on the label - available from most chemists.
Orangeflower or Rose water - frequently available from chemists, Boots has a Rosewater Toner in the Botanics range at £3.99 for 150ml online so must be in the shops.
(both these floral waters are often found in cookery ingredients shops, especially Asian shops but I've never tried them on the skin).
Nivea balm often gets a mention. There seems to be a few options in this range but I expect most come under the £5 mark. If you are talking about widely and readily available gear then I reckon this would fit the bill.
Well there are often offers on the likes of Old Spice and Brut to bring them into that range. Aquatonic AS is available from Asda I remember I picked some up for a quid, not bad stuff and there are the Gillette series balms.
Trevor Sorbie post shave balm,£4.99 from boots,and Kings Black Pepper & Sandalwood face balm also from boots,it's a little more at £5.99 but with the three for two offer at the moment it comes out cheaper.
There is a store locally called Home Bargins and they are selling The Ultimate Shave Facial Scrub, Moisuriser and Aftershave Balm for 29p each. Its suprisingly good even at twice the price. They also have Erasmic shave stick at 49p.