imo with a 100$ I think modern is the obvious choice. If it was me I would focus on the AR and the CHR from the last couple sets as the art is beautiful and is cheap so a lot of variety. The last time I checked ARs are a few bucks each. Obviously a binder is also needed.
https://www.elitefourum.com/t/jp-special-art-pokemon-card-gallery-sv/40918
This thread was very helpful for me making a binder of ARs.
You can also throw in a couple boosters for that opening fun.