Hi there!
One other thing to consider is your community and what it can spend. It's walking a line between trying to raise as much money as you can, but also appreciating what your parents are willing/are able to spend.
I can answer that! It is a game of chance - you have 25-100 bottles of wine, wrapped so that guests can not see what type of wine they are, and you sell opportunities to select a bottle at random. The opportunity is a fixed-price item - it's conceptually similar to a raffle ticket. The guest picks, then sees what they got.
You're welcome! And for the record, I agree with you completely - you do need to consider your audience, and adjust your strategy accordingly.
Personally - I was PTA President and then auction chair at my son's elementary school, which had a similar mix to what you are discussing (we had 39.8% of the kids eligible for free/reduced lunch - JUST under the cutoff for Title 1 funds), and I addressed the issue not through lower minimums, but through having a wide range of values on the items. We made sure we had a $10/slot signup party, and a $10 wine wall, and about 15% of the silent auction items had a Fair Market Value under $25. That kept the fire off me for having items with $35 minimum bids and $10 minimum raises.
I'm also a firm believer in having the number of silent auction items be about 70% of the number of bid numbers you are planning for - not everyone who attends is guaranteed to win something, so if you want it, you'd better bid - but making up for that with ample signup parties, wine walls, and a game like Heads or Tails.
Sounds fun! 
