While this is most likely much too late,
Henrys Tacos on Tujunga and Moorpark (if I remember correctly) is cheap, more or less tasty if Taco Bell like, and you can sit outside on the picnic tables if the weather is nice. Now the best part, if tacos or lack of conversation haven't killed the date by the time you are done eating, just adjacent is a killer dive bar called the Starlight Room for nice cheap drinks. Last time I was there it was one of the regulars birthday, and we all had cake.
Dude, that's not just a cheap date, that's depressing beyond belief. She will want to kill herself...or, if she has any self -respect, you.
Better cheap date: Caioti pizza, just catty-corner from Henry's Tacos. Split the BBQ chicken pizza, made by the inventor, who (you will inform her), invented it at Spago, later building California Pizza Kitchen's menu around it, & take advantage of their free corkage to enjoy a bottle of TJ's best. Peruse the scrapbooks full of the thank-you notes of grateful moms who finally delivered after partaking of "The" Salad (famed for inducing labor in post-due moms-to-be), quite helpfully introducing thoughts of the wonderful things sex with the opposite gender brings into our lives. After dinner walk next door in either direction: South, have a really good gelato. North, a really good dessert at Aroma. Then take her home to check out the latest in your Netflix queue, both of you giddy on Italian ice, 2 buck Chuck & great carbs, and let the magic begin. Total outlay for two: well under $20.
But...Henry's tacos? On a bench under ugly fluorescents? And Starlight Room? Again, fluorescents and paneled like your grampa's basement?
Both of you will swear off sex for LIFE.