Some quick calculations about TFLOPS per dollar on GEMM.
Since NVIDIA's volta consumer card is not out yet, I used Titan Xp as the reference card. I grabbed prices from wikipedia, and assume TVM reaches 64% peak perf on Vega and 90% peak perf on Titan Xp:
Radeon RX Vega 64: 12.6TFLOPS * 65% / $499 = 0.01638 TFLOPS/$ Pascal Titan Xp: 12TFLOPS * 90% / $1200 = 0.009 TFLOPS/$
So Vega outperforms a lot here.