The best place to eat here is definitely Riga Market. In the older, touristy section of the city, it´s hard to find somewhere for less than 13 euros a plate but in the market there are several mini cafeterias with super cheap dishes. The market is located right on the riverside. I recommend the typical drink wich is a wort. It´s a beer that has been fermented so it´s non-alcoholic and really good.