It will vary according to where you are based.
We paid 0.5%, which included advertising and signage, plus VAT in Portmarnock (Property Team). Sherrys quoted 0.7% (open to offers) and Remax 1%.
As sheena1 says, there are many existing threads.........
And btw, the auctioneer takes their fee, from the booking deposit, so in theory, there are no 'upfront' costs.