I have collected and sold autographs for many years and it is a weird business. It's "worth" is whatever one is willing to pay for it. Many names you got are not top dollar autograph names per se, but names like Tanner make it more $$$ appealing because you cannot get it. For example a dealer is more willing 50.00 for Anderson than someone like Randy Couture. Randy is more generous with his time and signs more autographs than Anderson s they are worth more. You have a lot of fan friendly guys and that decreases the value. Plus it is on a shirt which is also a value decrease. Best items to have signed for resell would be event posters and gloves.
As a fan I think you have a awesome object and would not sell it either. I never sell my personal stuff (most items from my favorite fighter, wrestlers etc I always get them personalized)unless times are tough. For example I just sold a Ray Mancini glove for a fraction of what it is worth to help pay the bills since I lost my job. You are a lucky person But with 50 names and photo graphic proof 500.00 is a very good estimation. Matt, Evan and Penn are worth most of that on their own. Congrats on the awesome shirt.