Hi @chinchi,
Some ideas, especially if your mom has FTC-level tastes (and can appreciate good food)… 
-
Inaba - Tempura specialist. If you’re careful about what you order (i.e., none of the fancier shellfish, etc.), you can have a comfortable, delicious meal and with Housemade Soba Noodles to finish things off for about $30 - $35 pp, maybe cheaper depending how much everyone eats.
-
Kagura - Tonkatsu (Deep Fried Pork Cutlet) specialist. I think you’ve been, right?
That should be right in the price range and they have some quiet tables on one side of the restaurant. -
Torihei 2.0 - Not as great as it was when the 3 original chefs were running it, but still respectable and quite affordable. I think our last meal there was about $33 - 35 pp (before Sake). Solid Yakitori and Kushiyaki (Grilled Skewers of Chicken and various veggies over Binchotan Charcoal, which seems pretty accessible to anyone).
-
Izakaya Hachi - Charming neighborhood Izakaya (Japanese Pub) with small plates.
Hope you enjoy your visit!