Who said you can’t double your salary in one career move? If you don’t believe you can then who will believe you’re worth it?
Once you have packaged yourself up into a killer CV you should feel immediately more confident. A salesman appreciates good marketing material after all. Working on your confidence is a key step towards making that career jump plausible.
If you feel confident then the person you’re speaking will be instilled with the same confidence. Aim high, if you have the skills then why aren’t you worth double? If you can ooze and win confidence then you’ve near enough won the game.