When I post auctions I always set the bid and buyout price to the same amount because I don't want people bidding on my items. I wish there was a way to do this automatically so I don't have to type the same amount twice for every auction I post.

My suggestion is: if you empty the bid price input field, when that input field loses focus, copy the contents from the buyout price.

In the tbc beta version I've added a feature where you can right click on the bid input to make it the same as the buyout value and vice versa.

By default, this is exactly what Aux does.
To have a bid different from the buyout, you have to activate some parameter.