This is kind of subjective. Specswise it looks like a fairly authentic setup, other than the HDD having been swapped for a much larger model (systems this old wouldn't have had an 8 GB HDD, much less 80 GB!). RAM is also clearly maxed out from a "period correct" 16-32 MB. That's fine. For me what's not really on the paper matters a lot here. Is the case tidy and well kept, or is it dented, scratched and yellowed, etc. Are there other novel features? Is a monitor included?
People were giving systems like this away not long ago, so the fact that someone is asking for $100 means they've either caught on to the fact that they're considered collectible now by some, or it's a person who's actually held on to the system and has a personal investment in it. I'd rather buy from the latter type than the former.
In the end whether it's worth the asking price comes down to how badly you want one now. I guarantee if you wait you'll come across something like it practically for free, from someone who just forgot to get rid of theirs. So in that sense the system is definitely not worth a $100.
Also, I wouldn't trade the GPU to a Trio/Virge. The Rage II is just as well, unless you have a very specific game that's incompatible for some reason (like your Commander Keen or something).