The baseball Barry Bonds smacked for his last-ever home run is hitting the auction block ... and it could fetch $750,000 (!!!!!!!!!) -- TMZ Sports has learned.
Baseball's home run king launched the final dinger of his career -- No. 762 -- on Sept. 5, 2007 ... when Bonds took Rockies pitcher Ubaldo Jimenez deep at Coors Field in Denver.
It was a mad scramble to catch the ball -- and turns out, for good reason ... 'cause the first time the ball went up for sale back in 2008 -- it sold for $376,612.