You should be able to get a Yamaha F310 for a touch over £100. Whilst nothing can be guaranteed, there's a good chance the Yamaha will be that bit better value-for-money than something that's costs just a few pounds less: it should be well-finished and will probably play quite well straiht out of the box and also sound half-decent. Worth considering if you are buying online.
If your friend decides that guitar is not for him, he'll hopefully get a reasonable amount back for the Yamaha.
Edit: Also budget for a tuner (unless you can len him one?), packet of spare strings, a few picks. Also maýbe a stand so the guitar is out and handy to grab and play (and prevent it falling over).
Look at justinguitar for lessons, get the basics nailed!