Limited supply at launch is normal, and there are better options for mining.

The long waited vega architecture is finally here, in the form of RX Vega 64 and RX Vega 56 slated to arrive on August 28.
I saw a $500 card at Newegg yesterday morning, but it has since disappeared. Not that it really matters, because all of the Vega 64 cards are currently out of stock.

Last summer when the gtx 1070 nad gtx 1080 launced, it was impossible to find them close to MSRP for quite some time.
Same story with the radeon RX 570 and RX 580 which continue to sell at more than $100 over their initial launch prices.

Here's the reality check: despite rumors and claims of Vega doing 70-100 MH/s (in Ethereum), in practice it's far less impressive right now. Using Claymore's version 9.8 miner, at stock I measured around 31MH/s on the Vega 56 and 33MH/s on the Vega 64 (I've seen a few claims of 35MH/s for Vega 64 at stock). That compares to typical performance of existing GPUs, using the same software, of 24MH/s for the RX 570 4GB, 27MH/s on RX 580 8GB, 21MH/s for GTX 1060 6GB, and 29MH/s on GTX 1070. Higher is better, so that means Vega is the best solution now, right? Not so fast...

Mining is not all about the performance its also about the cost of the power and the cost of the hardware.
Most pro GPU mining is done on a rig with 6 gpu.Cost of power and is power use are also factors, the latter of which requires a bigger (more expensive) PSU, or at least multiple smaller PSUs. Putting six 1060 6GB cards in a rig with a good 800-1000W PSU isn't a problem, and six 1070 or RX 570/580 cards in a rig with a 1000-1200W PSU would also work. But when Vega 64 can draw around 275W of power per card, you'd be looking at 2000W PSUs, or five GPUs with a 1500W PSU, or a pair of 1000W PSUs.

Even if the Vega 64 were readily available right now for $500, that's $3,000 in GPUs, plus another $800 in the remainder of the PC, for a rig that could do perhaps 210MH/s and use 1650W.A 6 1070 rig would get around 170MH/s .That's better hasing performance but the rig with the 1070 would use around 900W.
Using the current going rate of $283 for Ethereum, that's around $14 per day in gross profits from Vega 64, minus $4 in power costs ($0.10 per kWh), versus $11.50 gross and power costs of $2.20. The Vega rig would still be more profitable at approximately $10 per day vs. $9.30 per day, but even at the inflated $450 pricing of GTX 1070, going with Nvidia would be the better buy—$3,300 total for the mining rig compared to $3,800 with Vega cards. At $0.70 per day in additional profit, it would take about two years before the Vega rig would come out ahead. (Assuming current pricing and difficulty trends remain the same, which of course they won't.)