Sources

eurobasket.com

https://www.hoops.com.au/forum/46318-european-basketball-club-budgets-2019-20-season-us

https://www.eurohoops.net/en/euroleague/963346/list-of-season-budgets-of-euroleague-teams/

https://www.schoenen-dunk.de/topic/123071/etats-der-bbl-teams-2019-2020

https://s.lnb.fr/file/202009/budgets-masses-salariales-previsionnels-actualises-2020-2021.pdf

Each league's English Wikipedia Page for Attendances if available

https://www.easycredit-bbl.de/de/statistiken/zuschauer/zuschauer-statistiken/

https://www.2basketballbundesliga.de/zuschauerzahlen-proa/

https://www.aba-liga.com/news/41950/average-attendance-increases-over-2-600-for-the-second-time/

https://media.sportbusiness.com/2020/03/basketball-market-report-2020/

The other TV deals were checked individually by visiting each league's homepage. Translate in google chrome helped with the foreign language pages.

*FIBA International Basketball Migration Reports 2016-2020
http://www.fiba.basketball/documents - Studies & Facts

FIBA's Migration 2020 report gives information about the top leagues (page 27). Other sources are to be found on some league's websites in their statues. In cases we couldn't find the official ruling of the league, we checked the average of senior players with foreign flags on teams on eurobasket.com.

google search: most popular sport in X

https://www.fiba.basketball/rankingmen

https://www.fiba.basketball/rankingboys

https://www.nba.com/draft