James Harrison: I'll Bust Your Ass On a Boat ... For $900

Do you have disposable income ... and a penchant for pain??

Great news ... Pittsburgh Steelers stud linebacker James Harrison wants to kick your ass in a crazy workout routine ON A BOAT ... if you've got roughly $900 to spend.

Harrison is a featured guest on the 2016 Legends of Pittsburgh Cruise -- which sets sail from Miami to Mexico in February ... and allows guests to rub elbows with a bunch of past and present Steelers.

The cheapest room goes for $499 (plus $129 + $65 for fees and gratuity) ... but for an extra $199, you can join a cruise workout class led by Harrison himself.

"James will share his personal workout routine, diet & nutrition secrets," the description reads -- and if you follow James on Instagram, you know he's an absolute MONSTER in the gym.

Don't feel like working out on vacation? There's always the Gronk cruise ...