Well, nothing about your Land Cruiser will be cheap. For labor budget at least $500 for the rebuild. Parts will be more. Check justdifferentials.com for kit pricing. It makes sense to plan for front axle service and rebuild your diff while servicing your front axle.
Your best bet is to do the front axle service yourself so you'll need to order those parts. Also budget for new axles with as many miles as you have. Don't buy them yet - examine your axles to see if the seal wore a groove in them. If there is a groove then you need to replace them. Pull the front drive shaft while the axles are out and remove the front diff. Box it up and ship it to Zuk for rebuild - he's pretty fast.
Does your truck have factory elockers?