The contents table [0] which they ran the query on is 1.8TB. Assuming you only need to do a single pass (seems reasonable given that it's a simple regex), the price should be about $9 [1]. Free quota covers 1TB so the remainder would be $4.

[0]: https://bigquery.cloud.google.com/table/bigquery-public-data...

[1]: https://cloud.google.com/bigquery/pricing