plugs are actually about $12 USD each, however to change the rear spark plugs, you must remove the intake manifold and a lot of other misc wires and brackets. Wait till 100k miles and get them changed along with your timing belt.

 

I have a 2007 Mitsubishi Outlander and the mechanic is telling me to change my timing belt at 60,000 miles. Is this correct?

 

unless the belt as wear or is starting to fray....change it at 100k miles.

This pic is what my belt looked at 80k miles:
http://pictures.ccernst.net/Outlande...2011.34.36.jpg

When I changed mine at 100k, it didn't really look much different.