Reggie Bush -- Gets Mom $200,000 Bentley ... Happy Birthday!

He might be staring down the barrel of retirement, but Reggie Bush is making it clear -- he ain't worried about money -- 'cause he just bought his mom a brand new $200,000 Bentley.

Reggie's mom just turned the big 50 -- and to celebrate, the injured 49ers running back hooked her up with the keys to a sick Bentley Flying Spur ... which (depending on the options) can cost up to $250k.

Bush has reportedly made more than $60 MILLION during his NFL career -- not counting all of the endorsement $$$ he's racked up. Plus, he's planning on suing the city of St. Louis for a TON of cash over the knee injury he suffered there earlier this season.