Hasiguchi is far better than Nishichi.

One month in advance should be plenty of time.
When making the reservation it is best to include such requests as, “I plan to eat 15-20 pieces of nigari sushi, so please be sure to have enough fish on hand.”
There are many local customers who go there mainly to drink, so on some days not much fish is procured to make a lot of nigiri zushi.

In that case Is it better to tell my hotel concierge about my expected price range?

Yes, you better do.

I am deciding between Inomota and this one -- which one do you suggest?

Currently, I'd say that Inomata is superior in terms of both the toppings they use for their nigiri sushi, and the degree of care put into the making of the nigiri.