Are there any consumer-priced, single-band (5GHz / 802.11ac only) WiFi routers, i.e., ones that only have a 5GHz radio?
Routers and WiFi devices have to undergo certification to have the "WiFi" branding. Any router that does not have a 2.4 Ghz radio would not be backwards compatible with IEEE 802.11 b/g/n and may not qualify for the "WiFi" branding.
I have never seen a "WiFi" router with only a 5 Ghz radio. But you can disable the 2.4 Ghz radio in many routers though. It is possible that a router with only 802.11ac support can exist, but it may be hard to find a product like that using the "WiFi" brand as a search term.
For now, I would not recommend seeking out a product that explicitly avoids having a 2.4 Ghz radio. It wouldn't be guaranteed to work with other WiFi devices unless it was WiFi certified too. Some day the WiFi Alliance may decide to deprecate the 2.4 Ghz standards and this answer may no longer be correct.