Art,
Write your main contact(s) a nice email saying that you are sorry you lost their business, and if there is anything you can ever do to help them please don't hesitate to call or email you. Then check in six months and see how their service after the sale is. If their service is poor maybe your company can steal back the service. That does not help you immediately but the next time you put in a proposal you will NOT have to be the cheapest. Because they will have seen what cheap service looks like.
That's my $0.02
Vince