Pho Rua Vang
343 Booth Street (upstairs)
This restaurant is closed
This place, also called The Golden Turtle Restaurant, is across the street from the well known and very busy New Mee Fung. It is up the stairs from another restaurant, although there is no apparent connection between the two.
Their menu is quite large and cheap with prices mostly ranging in the $6 range. There is only a limited selection of soup sizes though - some have L and XL to choose from, while others are only one size.
UPDATE: As noted by one of the commenters, this place is CLOSED. See Pho Hoang Linh for another restaurant that has opened at the same address.