In reply to woolsack:
Couple of speedlights would be a good start.
If you've got a whitewashed room that you can get in a corner of, you should be able to control your bounce easily enough to give a nice even spread, thus negating the need for softboxes/unbrellas to an extent.
Like lots of camera gear, studio accessories are the sort of thing that you can pick up very heap if you search around.
I would imagine umbrellas are cheaper than softboxes. Reflectors are cheap and come in handy and are good for just a little fill.
Don't forget stands, should be able to get cheaply again.
Sub £100 might be tricky if you haven't got any flash/tungsten lighting yet though.