The fair value should be 100-130 assuming economy does not go into recession. This is caulated by assuming a reasoanble PE of 15. If economy stays strong, VST will have no trouble meeting the current projection.
Some panic selling may take this to 90-100 but that is the level can be tolerated.
With this, you can plan your entrance. I use ratio put spread starting from when VST was 150, and my breakeven is 125 and 100 for two separate trades.
If VST drops below 90 and economy starts to look like going south, then I may cut the loss and exit
