Believe it or not Home Depot has great deals on vanities. Use their website though as there are many more selection.

Also try Build.com
Good luck!

18.5" deep: https://www.wayfair.com/home-improvement/pdp/charlton-home-exquisite-home-36-single-bathroom-vanity-set-w001615493.html?piid=1476409590

with matching mirror: https://www.wayfair.com/home-improvement/pdp/charlton-home-exquisite-home-36-single-bathroom-vanity-set-with-mirror-w002101776.html?piid=1284875240