I think you need to re-evaluate both your budget and your priorities. Making $30k per year while paying $10k in rent is going to leave very little for travel. I'd be more worried about being able to buy food and clothing. Remember, you will have deductions from that $30k even though you'll end up not really paying any income tax. If you're being paid bi-monthly, each check will give you about $998 take home. Your monthly budget will give you $1267 for your monthly budget. Out of that you'll need to pay for clothing, utilities, bills, transportation, food and other living expenses. That is also excluding medical insurance and any retirement saving.

My point is, you might want to re-evaluate the idea of monthly travel home or to your girlfriend. You also might want to stick with whatever airline gets you the cheapest flight. Not my normal advice, but given frugal you will have to be to get by it is a reality.

My advice in general for you would be to have your girlfriend ante up for some trips to So Cal. Also, skiing trips to Tahoe are pricey and given that you're a student might not be the best use of your money. You live in SF bay area, there are plenty of things for you to do there in terms of vacation. Stay out of debt, stay away from using credit cards and don't end school in a hole from the start. Remember that most FT people here don't pay for their own travel. Their employers do.