Smirnoff is nowhere near the cheapest vodka. That's not a bottom shelf vodka. It is literally not on the bottom shelf of liquor stores. C.f. Popov vodka for literally _half_ the price of Smirnoff (and literally on the bottom shelf). Popov, by the way, is undrinkable.

Any vodka which is twice as expensive as another vodka cannot be called "bottom shelf."