What are the most common methods of determining valuation used by economists that claim Bit-Coin is on the verge of being a bubble I have seen many economists saying that bit-coin is highly overvalued and on the verge of a massive corrections.  What are the most popular models being used to determine the proper price for bit coin?  

I find it very hard to believe that these economists would base these opinions on this purely on conjecture based on the fact that bitcoin is a new technology, or not backed by a government.
There are two ways to look at the value of a financial instrument. One is the underlying asset base, the other is the yield.

Bitcoin has no underlying asset base and no yield.

Therefore, its only value is whatever people imagine it to be.

In other words, it's completely overvalued. But that does not mean it is on the verge of massive corrections. There is an old saying (attributed, as they often are, to Keynes) that the market can remain irrational for longer than you or I can remain solvent.