Auctiolator is an app that helps you with the price structures of auction houses. It estimates the total to pay to auction houses when you bid on lots for sale. Simply, you can set a max total you can afford to pay, and then receive a hint at when to stop at a hammer price that would not take you beyond your budget. Conversely, the tool can also prevent you from being over-cautious when bidding against others.
The app accounts for additional fees such as Buyers premium, Artist Resale Right and Value-added Tax. This free app also exists as a website called www.auctiolator.com.