A big percentage of bathrooms end up in "seaside" decor territory. It's a natural fit and I'm fan if it's subtle.
This powder room design has nautical-inspired stripes, brass hardware, and clean white. I've included all the sources for you below. You can get the entire design for under $500-- under $150 if you don't need the sink!
$25 Distressed Gold Mirror | Kirklands
$59 Broad Stripe Rug | Urban Outfitters
$20 "March Fox" Print | Amber Alexander
$14 Nautical Mini Pendant Light(s) | Home Depot
$18 Pearl Embroidered Hand Towel(s) | Pottery Barn
$330 Pedestal Sink | Kohler