I think it is regular PETG not Prusament. The Prusament PETG is more expensive than regular PETG. I just bought a roll of regular PETG and the price was 21.93 and with discount 20.89. Mathematically it works out to .95% of the original price. edited to correct my math after login and 2X check.
It was months ago, but someone else brought this up and i thought it had something to do with the website application of the discount to the price or something IIRC. it was a while ago, and good luck finding that post, but no nefarious activity was intended and there was a reason which was going to be corrected...
OP: I am sure Prusa is not running a scam to screw people on the discount.... (...fractions of a penny from the classic movie Office Space style
) bottom line, it is a very small difference and the price is what it is logged in and applied when you purchase.