If you are using the Harley grips that are "no glue", then the hardest part is cutting off the original grip on the left side. If you are using grips that glue on, then the hardest part is getting the right amount of glue on the left side without getting too much so it doesn't dry.
I've changed mine a couple of times now, and it's really pretty simple. It's definitely not worth what the dealer charges to install them.