As strange as it seems, downtown S.F. lacks decent cheap Thai food. There are tons of Thai restaurants in the area, but most of them are either too expensive or not very good (or both). Pad thai used to be one of my regular lunches, but my best and cheapest way to get a fix now is to bring it from home.
I like to stock up on Ethnic Gourmet frozen entrees from Grocery Outlet (lunch-sized microwaveable portions for $1.99), and my favorite is their shrimp pad thai. I need my remaining $30 to last seven days, so I'll do at least three home meals in the next week.
Ate: Pad Thai with Shrimp from Grocery Outlet
Remaining Budget: $27.26