I'd imagine something along the lines of...

Release: Plot of land available for 30,000,000 gil. Person can buy it out at that price.

6 hours later: Plot of land is reduced to 28,000,000 gil. Someone else can buy it out.

Basically it starts at a very high price and is reduced every few hours. The "bid" aspect is the fact that someone can buy out a piece of land at a higher price instead of waiting for it to drop. Kind of like a reverse auction.