SWE Intern Salary Negotiation.

So I recently received an offer for a Software Engineering Internship this summer for a company in the Bay Area. While I'm pretty happy on getting an offer, I noticed I'm getting low balled a bit. The offer is around $23/hour with a $1500 signing bonus over a span of 12 weeks this summer. Many of my friends in the same year as me are making well over $30 this summer, so I naturally want to negotiate up.

I don't have any other offers for the summer, but am still waiting to finish a final round interview for Salesforce. Any advice for negotiating up? $23 a hour seems pretty low in the Bay Area. Any advice would be greatly appreciated.