Well you need a barrel to brew it in, some stuff to sanitise your kit, and a hydrometer to know when fermentaion is done, a thing to put caps on with and then some bottles That's all the kit you need, £50 assuming you can source bottles, which is hardly difficult.
The to make your brew you just need a kit which is basically a bag of wort, and some yeast. £16.00 will do it, plus you'll need a kilo of brewing sugar at £3.00. Call it another £3.00 for 40 caps and it costs £22.00 to make 45 bottles (22.5 litres), so about 50p/bottle.
Obviously you've had the initial outlay, but that gets used again and again.
Serious home brewers do it far better, and they are many ways you can spend more money, but I'm churning out perfectly decent ale for very little money, and it really is very simple.