I looked at my favorite place for value... eBay. I'm sure you did too!
While I couldn't find a Plymouth watch, I did find a couple Dodge watches that are basically the same watch... The real tell-tale being the tin box.
One completed listing was $30 w/$10 shipping. Looks the same condition, not worn etc.
VINTAGE MOPAR DAIMLER CHRYSLER DODGE PLYMOUTH MEN'S WATCH | eBay
There are two women's versions of the Dodge watch, they haven't sold and are listed at $50 w/shipping included. (so $40 for the watch) from the same vendor. They have a history of selling two at that price.
Dodge Silver White Wrist Watch NOS Women's Quartz Water Resistant 31081 MPH | eBay
It's not a high end watch, made with a generic Chinese movement and most likely made as a promotional gift. The back of your watch is askew. Maybe the battery was removed or replaced, but not done by a pro. I just notice those things.
So, somewhere between $30 and $40 based on those eBay prices. Maybe a little less because the tin box has some dings that might matter to someone. I'd split the difference and ask $35... maybe take $25 if it's offered. If it didn't say Plymouth, it's a $10 watch.