Got into a conversation on Saturdays ride regarding the cost of decent MTB lights and someone mentioned (im not good with names) there wasnt much around for under £200.
Anyway for those interested after googling around a bit, you'd amazed at some of the lighting rigs people have setup for under £100 that give a Lupine Betty a run for her money, mainly based around Cree LED's emitters.
Lots of people currently raving about the tesco cree flashlight available for £10 (instore only). 3 of these (1 helmet, 2 bike) with mounts & rechargable batteries for about £70 make a nice starter rig.(search on the Bikeradar or singletrack forums for more info)
A step up in quality & price then come the Fenix lights [url]http://www.thephotonshop.co.uk/page61.htm[/url]. See some of the rig configurations here [url]http://www.ruscelli.com/biking_fenix.htm[/url] (well worth viewing!)
Alternatively buy the same direct from the US [url]http://www.dealextreme.com/products.dx/category.904[/url] or copies on Ebay at a fraction of the price.
There that should be enough to get people tinkering, have fun.