One of the most frequently asked questions I get is where to buy wig making supplies if living in the UK.
There are two main places that spring to mind:
Banbury Postiche - http://www.banburypostiche.co.uk
Hugo Royer - http://www.royer.co.uk/main.php
Both of these companies are located in the UK. As well as selling lace/tulle, galloon, needles, holders and blocks, they supply virgin European human hair. As far as I am aware, both companies can colour/texture match, which is particularly useful for making hair pieces that need to blend properly with the wearer's bio hair.
Banbury Postiche will sell you hair to practice with, but I personally have saved money by using old processed wig hair - Asian/Indian origin. If you have an old human hair wig that you do not want anymore, or some old wefts or just raw hair - you might as well use those rather than buy hair specially to practice making a piece or wig with.
If you are just getting started, you may also want to check out my first blog posts for tips on how to save money when learning and seeing whether you actually like wig making/have an aptitude for it. No point spending lots of money if you eventually find you do not enjoy making wigs or do not have the time.
You can definitely get away with a polystyrene head for purely learning ventilation, a needle holder, some needles and practice hair. You would not be spending more than maybe 20 to 30 pounds.