I agree that a raffle would be better than an auction to raise funds. However, if it must be an auction then I would keep it simple. You don't want to put 80 hours into something that will only sell for $100.
The last one I made for an auction was a twin size. I used one precut turnover (triangles) and used some yardage that coordinated with it. Just made a bunch of HST's and layed them out randomly with the odd solid colour block.
The bidders loved it, and it only cost me about 6 hours of time.