Will the AMD RX Vega be affected by the current bitcoin craze like the 1080 is?

My understanding is it's the AMD cards that are actually useful for mining, and thus the price of those are sky-high. The new ones are likely to be the same.

The Nvidia cards are only expensive because people can't buy the AMD ones, so are turning to Nvidia.

Sorry... That is not true! The Nvidia cards are actually better for mining Ether (where a lot of the current craze is) due to CUDA optimized mining applications. The Nvidia cards are just as good as the AMD competition at mining BitCoin as well. However, the AMD cards tend to be cheaper for the same raw performance speeds (That rarely translates into better gaming for AMD cards though as their drivers have historically been a bit behind) That does not matter for mining though. In an industry where coin price volatility is extremely high, and every cent saved translates into a faster profit turn around and cashing in, being cheaper matters. That is where AMD has traditionally been preferred for mining.

That is all not true these days however, now miners are looking to get their hands on whatever they can as its all translating into a potential cash in before Ether crashes to the floor. Its a race against the clock so everyone who thinks they will get rich with mining is racing to the door with the up front investments, hoping to turn a profit around 120 days after mining starts with the cards purchased.

AMD has had lower stock volumes on many of their products compared to Nvidia (Check the chip fab volumes supplied to each company) so AMD had lower stocks to begin with, and Nvidia is struggling as well to keep up. This will continue as long as Ether is a thing. This is a gold rush, and investors will throw all they have at the possibility to strike riches with their investments. Rest assured we will see DIRT CHEAP cards all over the used after market once the Ether craze settles. Lots of cheap cards will flood the market soon enough.

The DRAM shortages are not helping the GPU shortage situation any either.

TLR - All GPUs are subject to the mining craze until the prospect of over night riches dies off. That could happen any day. Likely will happen when all these adopters hit the 120 day mark of profitability with these cards and everyone tries to start selling and dumping ether in the exchanges for FIAT currency.