Most Sushi places in NYC are NOT Japanese (almost non existent on Seamless). While I enjoy some of those places, I simply don't them authentic. Here are some affordable authentic places I enjoy.
331 Flatbush Ave (btw Park Place & Prospect Place), Brooklyn, NY
Japanese Restaurant · Prospect Heights · 80 tips and reviews
Daiji: GEIDO is reasonable, and good. around since the 80s. go early. Don't ever end up at TARO across the street and down Flatbush... you will regret making a compromise.