Tamas πͺπΊπ¦πΉππΊ You can even make a scheduled payment on the first day of the month to get the new budget.
Unfortunately you can't make a scheduled transfer where you can say the amount must be the difference between 500 euro and the account balance. So it would be 456,78 in one month an 487,31 the next and so on. Hopefully bunq will implement something like IFTTT in the future so you can do these things.