Gilbert Arenas' NBA Contract Is Up, Claims He Can't Afford Private School

Gilbert Arenas' infamous $111 MILLION contract with the Washington Wizards is finally about to expire ... and Gilbert says he will be so poor, he won't be able to afford private school for his kids.

Gilbert signed the 6-year guaranteed contract back in 2008 -- but according to new court filings in his family law case, obtained by TMZ Sports, Arenas will get his last installment on October 31st (the contract was paid out over 8 years).

It was good while it lasted ... and Gilbert knew it when he spoke to our photog about the contract in 2013.

The problem, Arenas says ... is now that he's no longer getting NBA checks, he'll only earn $169,895 per year in investment income ... not enough to live the BALLER lifestyle he's used to.

So, Arenas says he has to make some serious cuts -- and one of the items on the chopping block is the private school where he sends his kids ... which runs $91,600 per year.

"I anticipate that the children will need to transfer to public schools in 2017 and beyond."

For the record, Arenas reportedly made more than $160 MILLION during his NBA career ... not including tens of millions in endorsements.