They would get an initial ~€300M for signing on [1], then a further €130-200M per year [2]. That presumably doesn't include matchday income, which could be a lot higher per match than now due to the higher quality opposition / teams involved. This would also presumably grow alongside the popularity of the competition.

Right now Premier league clubs get around €100M from broadcasting rights [3: this source is from a few years ago but gives a good breakdown of the clubs' income]. Broadcasting income is a lot lower in Spain and Italy, hence those clubs needing the ESL more. The ESL clubs planned to continue in their own domestic leagues too.

Here is a breakdown of the Champion's league money (which the ESL proposed to replace): [4]. Each decent team which reached the knockouts (so most of the teams involved in the ESL) would earn around €40M, with the winner earning around €80M. So winning the Champion's league would be worth less than simply competing in the ESL.

This all doesn't include sponsorship money.

Edit: I also want to note that of the 6 English teams, only 4 can qualify for the Champion's league every year. The others usually go to the less lucrative Europa league, for which the payout for winning is less than for simply participating in the Champion's league. This year those clubs were Tottenham and Arsenal - so even more benefit for those two clubs.

1: https://edition.cnn.com/2021/04/20/business/money-european-s...

2: https://www.givemesport.com/1678145-european-super-league-ho...

3: https://www.theguardian.com/football/2019/may/22/premier-lea...

4: https://www.goal.com/en-us/news/how-much-money-champions-lea...