Fixies have always been a fun subject of armchair economics. As late as '06, it was very rare that you'd come across track bike-specific parts. This was especially so with frames. Finding an old track hub in a used parts bin was practically winning the jackpot on a slot machine. Prices and competition for used parts was high, but mostly stable and flat. Ebay and track-specific forums were where you'd buy your parts; local bike shops hardly didn't even know the word 'fixie', let alone stock track parts (with it especially hard to find reasonably priced, non-Olympic competition level components).
The trend was growing quick, and folks started finding fancier and fancier vintage bikes as collectors realized that the market for the obscure bikes lit up like wildfire. At the same time manufacturers (big and small, global and local) began sourcing extremely cheap (>$300) frames from Taiwan and saturating the market, bringing prices down ~50%.
Then the Crash happend in '08. The market for fixies, mostly a semi-practical luxury item/status symbol similar to an iPhone at the time, fell significantly. They're still a big deal and quite popular, but not nearly as much so as a few years ago. Prices, especially the used market fallen drastically. A cheap, Average condition frame that went for $300 in early '08 could barely get $100 today in San Francisco.
Luckily for those who bought into the vintage/collector track bike market (like most), prices are relatively stable...