Fair Salary

We are a small charity and for years I have been the only employee. Now however we want to slowly grow the charity and I would like to take on an assistant, initially for 2 days a week.

I am completely out of touch with what would be a fair salary to pay and I am wondering if there are any guidelines anywhere on this subject, or if there is a current benchmark salary scale.

Any suggestions would be most welcome.

Thank you
John