Milk glass has been around for hundreds of years but became very popular during the late Victorian era. Oddly enough, it also came in colors like black, blue, and green. It fell out of favor during the Great Depression. In the 1960s, Fenton Glass introduced its Hobnail pattern; milk glass covered with raised, rounded dots that ushered in a new age of popularity. Companies created tons of the newly popular glass which were a favorite with florists.
The best value for milk glass is in older, Victorian pieces. One Atterbury covered dish that featured a boar's head recently sold on eBay for $910.00. Items with images of iconic cultural figures, attractive advertisements, sets, and rare pieces are valuable. Old French milk glass is particularly sought after.
I see plenty of late 20th-century milk glass in thrift stores for one dollar or less. The cheap thrift store pieces are popular to use at weddings due to their cost, the ability to match pieces that don't really match (they are all the same color), and their white color.
To learn more about the pieces you have, check out some books including:
"The Milk Glass Book" by Frank Chiarenza
"Collector's Encyclopedia of Milk Glass" by Betty and Bill Newbound
Once you identify your glass, shop for sold prices at online shops or auction sites for comparison.