10 years ago, people (including me) were using published manufacturing data, basic industrial engineering understanding of production cost reduction and industry growth trends to predict the rapid decline of cost of solar modules. Just like flat panel LCD display prices have plunged, so to have the prices of solar modules.
I think this guy (in the article below) is a little overzealous regarding 2014 pricing but $1.00 / Watt by 2012 for tier 1 mfg. is consistent with current trends and solar build out.
Look at Figure 4 in the 2001 paper below:
Cost Curves, PV Cost Projections