Yeah,you need a new mechanic. If it's that much of a hassle,then that means he can charge you more,so basically he's either lazy or not sure of what he's doing. The only time internal cables become an issue is when they need to be replaced,and that's not something you do on a regular basis.

The place where I bought my bike from said it would cost me $220 to replace both the front and back cables. I was so shocked of the price that I nearly vomited.

What bike? Your sig shows you have a '15 model;no way should that need new cables anytime soon. Can't speak to pricing Down Under,but here I can get a full set of high-end cables for well under $100US,and replacing them isn't a big deal. Esp if you're only replacing the cable and not the housing.

I will try to replace it myself in the near future if it needs replacing.

"Near future"? The only bike I have that could use a re-cabling is the Safari;it's an '06 with well north of 10k miles and has been ridden through many rain/snow storms and plenty of road salt. Unless you've got a MTB or cross bike that gets caked in mud every weekend,you're only going to swap the cables maybe 2-3 times in it's lifetime. By the time your bike needs it,I would hope you would have turned into a competent home mechanic.