if someone wanted to get into this kinda stuff and keep it under $600 USD, is there an entryway path or is not worth it at that level?
VCV Rack, hands down.
If you want to stick with hardware, Behringer have a few cheap, fun and effective semimodulars (standalone, no need for rack) like the Neutron and K2. Best Bang for the buck.
Arturia’s V collection includes a Buchla emulation. Personally I find it (the Buchla) impenetrable but YMMV. If you’ve got some MIDI controls lying around already you could have some moderately inexpensive fun.