Need help/input on private giveaway group rules?!

So I am gathering some info and trying to make a very solid private giveaways group. But this part is bugging me a lot. I don't know what's the best rule to implement to make the group maximum efficient - fair towards all members. So let's say if someone is really damn lucky, not that 1 person can win all games in a row.

I was reading a lot of rules in private groups I found around but was not really happy with that what I saw/read. So anyone with a good idea is welcomed. And I will try to implement the best one of them all.

I was thinking something like this: A minimum per month giveaway is 15p = 15$ on steam game value. So you giveaway a game of 15$ and earn 15p and each of your giveaways is multiplied by 2x. So 15P x 2 = 30P and you can use those points to win games. You can only enter games that have a value of 30$ or lower and if you enter that giveaway the points are on "hold". If you win then you wasted your points and can't enter anymore giveaways. If not the points go back to you and you can invest them further one. You can also split them and go 2 games of 15$ that's a 30P when you add them up.

Since it would be lame if you could enter 10 games each worth 15$ and you just spend 15$ yourself yet you can win them all if you are a lucky guy. Or if you spend 15$ and enter games that are like 60$. Dunno, I have a really hard time with this rule. I want to make it maximum fair and best for all in the group. Yet I don't know what rule would be best for this. So please guys/girls help me out. Even if you put a ratio rule of let's say 1.0 so that means how much you gave that much games you can win, but still it's not the same if you give a game of 5$ vs a game of 50$.

This is really complicated for me. Anyone with good ideas?