Two reasons it's expensive to repair your Mac:

1) The resale market is intense.  Even the early 2006 Mac Books regularly sell for $500 and up in the secondary markets on Ebay and Craigslist.  This drives up the cost for parts, which are often twice as expensive as their PC counterparts.  Keyboards are $50 and up, lcd screens are $150 and up, etc.

2) Apple does not want their products to be user (or tech) serviceable*.  They make a great product, but they are not meant to come apart.  As such, it can take even an experienced electronics engineer a number of hours to just replace a keyboard or hard drive.

Our prices at Computer Love reflect these realities.  We can, and often will beat the Apple Store by 20%, we cannot however fix your Mac at the prices we fix PCs for. 

*Although the "Ifixit" website (and others) are good guides, they are no substitute for an experienced electronics engineer.  Often times these guides gloss over the difficulties encountered when servicing an Apple product.