Thanks to foodiemonster's tip back in March, I have been on the lookout for the fresh rice noodle factory at Mission and 16th. I've been by a few times, but the door has always been locked, but today it was open! Just as foodiemonster described, I walked inside and was able to buy sheets of rice noodles by the pound. I chose not to have them cut, though they offered to cut them for me. I bought two very large sheets (total weight on 1 lb) for 1 dollar, and they were still slightly warm.
Not a store, and not very pretty, but an excellent cheap source for rice noodles closer to home - no need to go all the way to Chinatown.
Here's a link to the previous post, and thanks again to foodiemonster for the tip!
Kun Wo Food Products has a small sign, and it's on the south side of 16th St, between S. Van Ness and Mission. Just west of Bar Bambino.
Kun Wo Food Product
2939 16th St, San Francisco, CA