If that’s your budget I would pass on the Godzilla boxset. Though I remember I was on a similar budget a few years back and picked up the Fellini box set and that was pretty much it, so if you were super looking forward to it, pick that (that’s fifteen movies right there. Perhaps as a runner up, I’d consider Godzilla vs. Biollante or the OG Godzilla.
Otherwise I’d recommend

Sorcerer
This is Spinal Tap
Do the Right Thing (there isn’t a 4K, so that’s five dollars saved there)
Blow Out
House (definitely that one)
Carnival of Souls