Can I upgrade Numbers 1.0.3 on MacBook Pro with High Sierra?

As far as I can recall there never was any upgrade pricing to go from iWork '08 to iWork '09. Later versions, post-October 2013, have been available for free. However, as has been mention in this forum many, many times, only the current version of the apps are available for download from the Mac App Store.

You could have that person export the files to Excel format & sent those. Numbers will "translate" from one format to the other & the process may not be perfect.

Another option to open newer Numbers files would be to sign into iCloud.com & open the files in iWork for iCloud. Or, if you have an iPhone or iPad, use Numbers for iOS to work with the files.

The last version of Numbers in iWork '08 is 1.0.3. The update can be downloaded here. Pages 3.0.3 & Keynote 4.0.4 are also the last versions in iWork '09 & those updaters are also available for download from Apple.

I do not recall what the last version was of Numbers '08 (Numbers 1.0) before Numbers '09 (Numbers 2.0) was released. Support for old apps goes away pretty quickly.

If I recall correctly, back in the day you would download and save the update files (they came as disk images). You owned the install DVD so, if you ever needed to, you could reinstall fresh then upgrade to the latest release all on your own, without relying on Apple to serve it up for you again. Do you have any of those still around?