I’m really confused how you communicate with it? That seems like the most (expensive?) and technically difficult part.

I’ve got some cool ideas for atmospheric Reentry but I’d imagine there are all kinds of permits needed?

>I’m really confused how you communicate with it? That seems like the most (expensive?) and technically difficult part.

Not really. They typically use standard amatuer radio frequencies and protocols. Making space to ground contacts is doable with a handheld radio and directional antenna. Main limitation is low data rates (dialup or worse) and low coverage (you'll probably only get 1-2 passes a day from a single ground station). A decent semi-permament ground station can be built from off the shelf parts at a fraction of the cost of the overall satellite.

If you're interested in building something, Planet released an open source hardware/software satellite radio that works over amateur radio bands for ~$50: https://github.com/OpenLST/openlst

A combination of amateur radio operators, university ground station cooperatives (most universities with a cubesat program set up their own and join something like UniCOGS), open source ground station networks like SatNOGS, and commercial services like AWS Ground Station.

On the satellite it’s just an off the shelf UHF/VHF transmitter or SDR.