What is the average cost to install tile?

It varies greatly from product to product and from market

to market. The best way to get an answer is to put an ad on Craigslist

telling what you want installed, ie..

12' porcelain tile overwood subfloor,

new construction, 400 sq feet.

The lesson here is that the more detail you put in the ad, the better the quote.. You will have to understand that not every installer has Golden Hands, some are thieves & butchers, so you may not always want the low bidder..