I'm not sure what you mean - do you mean a minigame in /games that you have to pay gold to play? If so, I don't think people would play it much, since games are free to play.
I'm not sure I understand your suggestion, but the way I see it is the 4 players can each pay some gold - judging by what you said, I assumed you choose what you pay, unless you meant that the price is fixed and the amount of gold dropped would be the same as the price. Once the players were in the game, gold would drop, either from the sky or just appear, and you can pick it up and the person who picks up the most wins, but you get to keep the gold you pick up, I assume (since it's the same amount as what you pay).
I have a couple of questions about this - you said the amount of gold that drops would be the same as the amount you pay. However, there are 4 players in the game, so overall players would be paying 4x the amount that is dropped so you could, at best (which is very unlikely) not make any profit from it, which makes the game seem pointless, especially since you would almost always lose gold.
If you meant that the game would drop the amount that all 4 players paid together, then there would be a decent chance of making a profit, but you wouldn't gain much.
One of the potterworld rules is that gambling is not allowed (it's under inappropriate behaviour on the rules page). Keeping in line with these rules, potterworld has nowhere that you can gamble. This game seems like quite a gamble, as you are paying gold for the chance - but not certainty - of winning more gold.
If the amount of gold that you pay is down to you, which is the impression I first got when I read your suggestion, people would pay as little as possible to avoid losing anything, since you don't make more of a profit if you pay more. You probably meant it to be a fixed price, because it wouldn't work otherwise.
However, I'm not sure I understood your idea fully, so please tell me if I misunderstood.