2 More Things You Need To Know Before Hiring Startup Interns:
(1): Hiring season started last Oct/Nov for competitive tech internships. You're way late if you're starting now.
(2): You should pay more than $15-$30/hour for an excellent CS intern -- rates are increasing every year, even up to the monthly rate equivalent of six figure salaries at large companies (Facebook, Google, Dropbox, Amazon, etc).