By 18, I assume you mean Premiere Elements 2018.
The "upgrade" Adobe offers is actually just a special price for current owners of the program. You still get a complete, independent installation of the program. Whether this special price is applicable to version 13 is worth a shot. Worst they can say is know.
But meantime keep your eyes on Amazon and other outlets, especially during Black Friday and Cyber Monday sales. You may be able to find the program even cheaper than the upgrade price.
Thank you, thats helpful and a good idea!
It is currently $60 at New York's B&H Photo. As a New York store they normally don't charge sales tax outside of New York state. You can get the disc or download.
From previous experience, this is the rock bottom price for the year.