For a newly registered domain I like this one. But admittedly I'd prefer the plural version lockchangers.com, because it implies a team working to change locks whereas lockchanger.com implies that it's a one man business or refers to service.
Of course, if you pick up lockchangers.com you'd want to pick up lockchanger.com as well and redirect (similar to how namepro.com redirects to namepros.com).
I'd say $500 to an end-user. The main issue with these EMD:s is that it's limited to a niche, so it might be hard to find a buyer.