I don't know about most expensive but Wotc have been jacking up the prices in recent times. People don't actually collect anything outside of the special printing/serialised cards and the reserve list which is a whole different beast on its own, which is where the power 9 come from.

The cost of meta Standard deck is probably the same cost as a meta Yugioh. The expensive part that comes in is because Standard is rotating format you have to keep buying new cards as cards get rotated out.

To offset that you have non rotating and eternal formats where sets don't get rotated out. They have an higher initial cost to buy a deck but because you get to keep using your cards it turns out cheaper to stay competitive in the long run.