Are you referring to the Archived old Arena? We had to upgrade the database and it wasn't all portable to the new one so had to be left behind as read-only.
However, as mul-ta said, prices do fluctuate. This is especially true of Nirvanas as in addition to the ebb and flow of popularity that all ponies get, there is the ebb and flow of supply as new locations open up or an influx becomes more scarce. For example Argentina and Greek ponies were quite cheap MOC for a while a long time ago, but as the supply has dried up, prices have of course increased, substantally in some cases.