What board to charge

[Whoyoutakingto]

Single parent and work full time. 2 youngest 21 and 22 back from uni. One starts job in a week 1 in a month. They know they have to pay board when they get their first wages, originally I said £200 a month but now I am wondering if that is enough?
I looked through bank statements and it works out last month I paid £480 for just shopping. I will probably have to also take DD to her job and pick up as we live in a village with rubbish public transport. Job about 5 miles away.
We live in the North West so luckily it is relatively cheap here. I am not looking to make a profit but I don’t want to be out of pocket either.
Suggestions please.

Our son is in his first job since graduation. We are taking 25% of his take home pay. We are going to bank it separately with the possibility of giving it back to him when he moves out. We are both early retired and have good pensions and no mortgage so in a comfortable position but the reality of life is you have to pay your way.