First off, welcome to the forums! What a nice find. Barn finds are getting so rare these days.
According to Hagerty's, if the bike is in #1 concours condition, then it could be worth as much as $4,200.
Most of them sell for $1,500-$2,500 depending on condition.
Here is Hagerty's definition of #1 concours condition:
Condition #1 motorcycles are the best in the world. The visual image is of the best motorcycle in a condition often better than when it left the factory, riding onto the lawn at the finest concours. Perfectly clean, the motorcycle has been groomed down to the tire treads. Painted and chromed surfaces are mirror-like. Dust and dirt are banned, and materials used are NOS or original and superbly fitted. Early 1900s original barn find motorcycles with excellent sheet metal and good original paint that are running and clean can fall into this category. The one word description for #1 vehicles is "concours"
PS, you will need to replace the tires for safety reasons. Rubber hardens with age and loses its grip. Also ALL fluids need purging and replacement, but it will be worth it for sure.