Accecity2009 via eBay offers this Hairdressing Barber Salon Cape for $1.99 with free shipping. That's pennies under our mention of a slightly larger cape from two weeks ago and the lowest total price we've seen for such an item. (It's also a current price low by at least $2 for a similar cape, outside the mention below.) It purports to be waterproof and measures approximately 49" x 31". Expect this item to arrive in two to eight weeks.
Of note, some other eBay merchants have similar for around $1 more.