It's all guesswork but I very much doubt Foster was on anywhere near £50K a week even when he was at Man United as a backup GK back then that rarely played. I'm pretty certain he wouldn't be getting that at Watford or West Brom. Maybe you mean £50K per month??
that's far more realistic.
But regardless I get your point, and I thought the same he is probably happy to be involved. Great for his already impressive online presence being involved with Wrexham, a very likely promotion, and a netflix series. My guess £5/6K per week.
What was smudger on at Notts? £500 pw? I recall him saying that either he didn't know or didn't care.