"On" versus "off"

Solution 1:

There's a bit of a tangle here. The three players are:

• savings on name-brand clothes
• a savings of 75%
• 75% off

A. “Get savings of up to 75% off name-brand clothes…”
= “The savings you can get on name-brand clothes are up to 75% off”

Option A simply omits on. Arguably it's kinda awkward: saying the savings are 75% is much nicer than the savings are 75% off, unless you're about to say …off list price or something, but then I'd likely prefer 25% of list to avoid confusion.

B. “Get savings of up to 75% on name-brand clothes…”
= “The savings you can get on name-brand clothes are up to 75%”

This is the option I'd go for. Straight to the point.

C. “Get savings of up to 75% off of name-brand clothes…”
= “The savings you can get off of name-brand clothes are up to 75%”

…No.

Solution 2:

The second sentence is the most correct of your options, since the savings is not off the clothes, it is off the price of the clothes.

Solution 3:

The first option may not be logical but it is idiomatic and it's what you usually hear:

OPTION A "Get savings of up to 75% OFF name brand clothes..."

What's happening here is probably linguistic elision, i.e., "[Buy now and] get savings [that amount to] 75% off [the price of] name brand clothes."

In rapid-fire ad-speak, this is normal and universally understood. You'll also hear "on" but "off" is probably the more-common usage.

Solution 4:

How about just "Save up to 75% on name-brand clothes..." ? Or is the "Get" really important to you? Or you might use "discounts," as in "get discounts up to 75% on name-brand clothes...". But if it has to be one these choices and it has to be correct, I'd go with A.