50 Cent -- I'm Making Big Money Off Mayweather/Pacquiao

50 Cent is jumping on the money train this weekend, where he plans to score huge bank off the backs of Floyd Mayweather and Manny Pacquiao.

Club sources tell TMZ ... the rapper is getting half-a-million bucks Friday night for throwing down rhymes at Drai's.

Fact is, 50 may be hedging his bets. You may recall ... he's put $1.6 mil on the line, betting Floyd Mayweather will put Manny Pacquiao in his place.

And we're told he also made a deal with Effen Vodka to make around $500k for a show 2 weeks later at Pool After Dark in Atlantic City.

When it rains it pours.