G'day mate,
I have kept Yellow Faced Whips on and off for about 4 years now.
They are normally fairly cheap when available - $100-200 each. The hard part is getting them to eat anything other than skinks. They are incredibly active, slender snakes and will escape through ANY gap.
I have been swapping info with a few other people who are mad about small elapids like I am, and some have had success weaning them from skinks, to fish, and then onto mice. It is a long, tedious process though. I would recommend practicing on Tigers or Eastern Browns first, to get the knack of getting them feeding down. This may not be possible if you aren't permitted to do so? If not, try on species such as Green or Brown Tree Snakes.
Cheers
Jonno