8:09 AM PT -- After further review, David Kohler tells TMZ Sports he and his SCP Auctions team now believe the ball would sell for around $500,000 if it hits the block.

The man who pulled Shohei Ohtani's 50th home run ball from a scrum in the stands of LoanDepot Park on Thursday afternoon is about to be a whole lot richer ... 'cause, according to auction experts, the keepsake is worth a small fortune.

David Kohler, president of SCP Auctions tell TMZ Sports ... based on their initial evaluations -- the baseball that Ohtani socked over the left field wall during the Dodgers' blowout win over the Marlins will likely sell for over $300,000 on an auction block.

While a hefty price tag for sure, the piece appears to be worth every penny ... as it's truly one-of-a-kind.

It marked the first time in baseball history that someone has recorded 50 home runs and 50 stolen bases in a single season. It also was part of a game that some are calling the greatest ever played -- as Ohtani finished the day with six total hits, three home runs, four runs scored, 10 runs batted in and two steals.

As for the owner of the ball -- they've yet to be publicly identified -- but a witness at the stadium told cllct on Friday he's believed to be in his 50s.

Reportedly, the guy went through negotiations with the Dodgers after securing the ball ... but he ultimately left the stadium with it in his possession.

No word yet on what he plans to do with it ... but if he does want to part ways with it -- he could apparently land himself more than a few steak dinners, sportscars and designer bags in return.