The one thing you have in your favour is that we're entering warmer months (in theory
) so your original outlay won't be near that if you were starting in the winter.
Clothing:
Merrino base layer or at least something with 'wicking' properties (makes a world of difference)
Light weight walking trousers, maybe a pair that converts to shorts.
Teeshirt (long or short sleeved)
Fleece / hoody
Lightweight jacket
Cheap set of water-proof over clothes (trousers and jacket that pack into one). Sprayway or Regatta.
Socks - a thin Merrino walking sock that allows the feet to breath (not a base layer sock though)
Either walking shoes or approach shoes (Adidas Terrex is my personal preference)
Gear:
A 25L rucksack
A basic first aid kit (don't under estimate the need for this)
Drinks and snacks. Water to Go type bottle if walking near rivers etc.
Not essential, but for around £30 you can get an emergency shelter which will keep you dry if caught in a downpour. Weighs next to nothing and beats getting soaked to the skin an hour into a day out.
Sports Direct, Decathlon and Go Outdoors are good shouts for getting kitted out on the cheap.
Enjoy