Grill pans are really common to find in thrift stores. I’ve never met anyone who actually uses one regularly but like all good cast iron cookware, they are collectible.
The most recent style of Lodge Grill pans have flat top ridges as shown below.
The early (Discontinued) variation by Lodge had pointed ridges! Apparently food sticks to the pointed ridges too well so they were replaced by flat top ridges.
Have fun with your cast iron collecting!