I am in the same situation like you, but was admitted for Structural (Civil) Engineering MS.
After you accept the offer from Berkeley and get officially registered you'll be able to apply for TA and RA positions. However, I've heard that those are limited and you are more likely to get hired if you are planning on going for PhD. If I were you, I'd still go to Berkeley. Sooner or later you're gonna make the money to pay the loans off but the degree is something that you'll keep for the rest of your life. Switching fields is sometimes beneficial but in your case I wouldn't do it.