I did some more research and asked a connection of mine working in Binance (marketing dept - EU): he couldn't share exact figures but said to focus on the 100-200$ range

I also checked Newbanks and their CAC is around 40$ (at least, in Europe).

I also find this whitepaper

https://morfin.io/wp-content/uploads/whitepaper-v5.1-1.pdf

pretty detailed and they estimated a 14$ CAC (too low)

Overall, for my analysis I'll take the 100$: I know that numbers can be improved with SEO and good affiliation but this would take too long for the investors I'm talking with.

Now I need to focus on the average return (which seems very hard to compute)