[Avenger42]

> do you really want to walk away after the effort you've put in to this point?

Can you afford not to? The company you're dealing with has now proven to be unwilling to stick to the points you spent all that time negotiating. They're counting on you conceding the $10 because it's easy.

Unless you show that you're willing to walk away and start all over from scratch (preferably with someone else), they'll push as hard as they think they can get away with.