UBI, by definition, is an fixed, unconditional, income. If it's need-tested (such as scaling by a formula taking into account local cost of living) it's not a UBI, it's a conditional, needs-treated welfare program. UBI is specifically intended to dodge bureaucratic overhead by avoiding means-, needs-, and behavior-testing common in existing welfare programs.

So the "alternative" you propose is actually what a UBI is by definition.