I find them, typically, at rummage sales and thrift stores and have never paid more than $4.99 for one, and most are around $1. They were popular tourist trinkets in the 1950s and were made for most states, large cities, and national parks. I've found some odd ones, like for the National Cowboy Museum in Oklahoma, and, for some reason many local churches marked significant anniversaries with commemorative plates.
Events like the Seattle World's Fair in 1962 (when the Space Needle made it's debut) were also popular to memorialize in a plate, and the dimensional relief on this particular piece if pretty great. They often hung on the walls of people who bought them, servings as memories of family vacations and roadtrips, made doable by the automobile in the mid twentieth century.
The plates went out of fashion and people are getting rid of them now, gifting them to the Goodwill as they find them in old boxes of grandma's stuff. As a sucker for Americana and kitsch, I'm intrigued by the architectural features and natural wonders chosen to represent each state/city on their plate. It's telling of the time and era, and also acts as a historical document, as this New York City plate does, with the Twin Towers standing tall pre-9/11.