My 24yo son moved back in with me. He thinks he should pay nothing since he's my son. I told him 750 for everything. Meals, bills etc.
Is this too much for a kid that takes home 1k a week?
That is way more than fair. It's less than 25% of his income, and I'm willing to bet his meals are cooked for him. As an exercise, have him do a search to see what kind of place he can get for $500. The additional $250 is food, utilities, and the like. He'll be pretty shocked. And thinking he can just move home and live for free is not the actions of a 24 year old man.
Whenever my kids are home and working (summers right now) they pay (very little. $300/month). I have an account for each of them. All of their "rent" money goes into it, and when they get to a point where they're going to buy their own place, they get it all back. I started charging rent once they were 18 and had a job. By the time they are at a point where they're looking to buy, there will probably be around $5K in their account, and they will get it all as a bonus when they buy a place. Imagine how nice it would have been when you bought a house to get $5K in cash.