SELECT 1/mean(“price”) in Flux?

SELECT 1/mean(“price”) AS “mean_price” FROM “feed”.“autogen”.“match” WHERE time > :dashboardTime: AND “pair”=‘ETH-BTC’ GROUP BY time(:interval:) FILL(null)

I believe this should give you what you’re looking for. Flux doesn’t support InfluxDB 1.x template variables, so you’ll have to hard-code the time range and window interval.
The example below queries points from the last minute, windows (groups) them in 5 second intervals, and calculates an average for each window.
It then divides 1 by the result and stores it in the _value column.

from(bucket: "feed/autogen")
  |> range(start: -1h)
  |> filter(fn: (r) => r._measurement == "match" and r.pair == "ETH-BTC")
  |> aggregateWindow(every: 5s)
  |> map(fn: (r) => ({ r with _value: 1 / r._value}))