discount to vs discount off vs discount off of vs discount from

To get the full A app company experience, we recommend you upgrade to our paid version (at a substantial discount TO list price).

I found that sentence on a website of an app company and the preposition 'to' is confusing to me. I guess the whole sentence means if the original price is 10 dollars, users can get a huge discount like 30%, 50% or 80%. My question is can I change the preposition having the same meaning as follows?

a. at a substantial discount TO list price
b. at a substantial discount FROM list price
c. at a substantial discount OFF list price
d. at a substantial discount OFF OF list price

Are the four sentences grammatically correct and interchangeable? I am also wondering which one is frequently used most.

Solution 1:

The standard expression appears to be discount on (see https://www.writing-skills.com/discount-on-discount-off . To could be read as meaning compared to. Off of is definitely nonstandard English.