Inmates can spend between $50-75 per week at the commissary but that doesn't include telephone time. You should be careful with your budget and make sure that you are taken care of first. The prison system does a very good job of clothing and feeding the inmates. The commissary is for the "little extras" that help out. If you can spare $25 a week, that would not leave him hanging and would be enough to make his shopping at the commissary satisfactory.