You can go back to early 2014, but the masternode effect hadnt kicked in yet. And you can chart it against BTC so that its volatility rubs off on dash. However, this is what  it looks like in USD, since January 2015,  when the number of nodes was still quite low:

image gratuite

Correlates relatively well with the #masternodes:

image a telecharger gratuitement

There hasnt been a test yet of a significant price drop since the masternode boom, nor a test of market price during a non trivial masternode count decrease. Of course, these things will almost certainly happen together. And we know how that ended for all previous PoS coins.