I interned in Minor League Baseball for a summer and got paid NOTHING!!! I worked 60-70 hours a week, had to pay for my credit hours, my parents paid for my apt and gave me a very small allowance for entertainment and neccessities.
Not only did I do my job in the Souvenir store and Merchandising dept, but I also pulled tarp and learned stadium operations and groundskeeping. I did go on and work for the next 4 seasons in Minor League baseball and for a small salary each year and I have no regrets to this day. I also received the Intern of the Year Award that year for my College; for the work I did, the hours I put in and the journal of my adventures which apparently made the professors laugh at some of the things I encountered that summer.
In my professional career, I have seen a monthly stipend of $500, I have also seen an hourly rate of upwards of $12 an hour. I would start with your industry and your resources there and get ideas from those in your area of what they do. Have you tried just searching on the internet for it? Salary calculators based on the region and the industry? Good Luck