Any arrangements - should involve your input about what is reasonable.
If you are available to work those hours every week - then the hourly pay is something that you would consider - no matter where you are working.
Is $5 per hour even the minimum wage?
What is the minimum wage - and when are increases due to occur.
If you were working for an employer then would there be money deducted to protect you - such as unemployment insurance, workers compensation, etc?
If you consider that you owe them your time/service for their financial assistance - then what is your time worth (in dollars)? Don't let them minimize your worth.
Don't let them dictate the conditions - you must have input too.