Mine did the same...seals were like $5-10 bucks. A shop will probably charge 1-2 hours labor so $70-$200 depending on length of time and hourly rate.

 

No reason this shouldn't be covered under warranty regardless of tire size. This happens prematurely even to stock jeeps. Make sure to look into that before anything else.

 

Don't just drive around spilling fluid on streets , or worse yet , on the trails . It's not that hard to fix . Get the best seals you can find as they are cheap . Don't buy cheap ones . Get Spicer axle seals. I can't remember if the ball joints have to be removed or not . but that would be the hardest part .