Does anyone know what happens when a winning bidder for an auction unit fails to complete the purchase within 90 days?
Are they ever given any extensions?

Will the unit just go back up for auction?
Or can an interested 3rd party buy the unit from the bank after the auction winner defaults on the auction purchase terms after 90 days.

depend on bank and whether auction is thru court

The unit will be reauction again. You can only buy via auction process. Bank will not sell to you direct.

Do bidders need to come out with any money (or deposit, for example) when bidding or after winning a bid?
Will they lose this money if they fail to complete the transaction?

When bidding, you need to prepare bank draft 10% of the auction price. After you win the bid, if you cannot complete the process within the required time provided, the 10% deposit will be forfeited.

I see. Thanks for the information. The whole process seems tedious to a layman like me, therefore it's kind if a deterrent even though bargains can be had.