Bike lights

I've noticed there is a weekly bike ride at 17;30 or round about that time in terrey hills. Now i was wondering if you need a bike light for these rides. I looked into buying a bike light and have been shocked buy the prices. One store told me they start at $140 which is rediculus. So my question is do you need it?

If the answer is indeed yes

where did you get the bike lights from? How much did you pay and what do you recomend.

My fall back plan is to go down to dicksmith electronics and wireing up a few LEDs.

Information would be aprecieted, thanks.