It depends on who's selling.
Williams is an overlooked brand by uninformed tool sellers. In part because it's known more by industrial mechanics and machinist than by auto mechanics. It's a quality brand (on par with SK, Armstrong, and Wright) that can go for cheap if the seller isn't familiar with the brand, but pricier if the seller is in the know.
I've been working on putting together a set from flea market finds and yard sales as well.
I started by accident when I needed a 1-5/16" wrench for a project. The Williams was the only one I could find quickly, but the seller would only sell the 3 largest wrenches as a set. He wanted $60 but I was able to talk him down to $50. All my others were bought for much less (pennies, in some cases).
That was 2yrs ago. If you rush, it will cost you more. If you're patient, you have time to look for bargains. Here's what I've scrounged so far.