Vietnamese food is both delicious & cheap in Silicon Valley. I would say it's authentic in San Jose, but I'm not qualified to judge how legit it is. Vietnamese food may not be as familiar as other cuisines in America, but it is one of the best comfort foods.
[1] - Here in NYC, there is a dearth of good Vietnamese food. NYC Banh Mis are easily $6-8 for a subpar product. Contrast that to paying $2.50 in Milpitas for a giant Banh Mi.
Pho (Beef Stock with Rice Noodles) - About $6 with satisfying broth and exotic cuts of beef http://www.yelp.com/biz/pho-tau-bay-san-jose
Banh Mi (Very Cheap French Baguettes Sandwiches) - No more than $3[1] and comes with your choice of meat http://www.yelp.com/search?find_desc=banh+mi&ns=1&fi...
[1] - Here in NYC, there is a dearth of good Vietnamese food. NYC Banh Mis are easily $6-8 for a subpar product. Contrast that to paying $2.50 in Milpitas for a giant Banh Mi.