I would think it would be fairly close in value to an L-23 of
comparable age/time/condition/equipment. It would probably go for a
little more due to the increased aerobatic capability. Look for L-23
ads on sites like Wings&Wheels and search back a year or two using
archive.org's Wayback Machine to get a larger sample. If you're lucky
you might even find a few actual L-13AC's for sale even though they
seem to be much less common than L-23's.