For the OP - read through that nav delete thread.
I'd describe the process as intimidating more than hard. It's scary anytime you cut off entire wire bundles, but the process is highly documented so if you can learn to reliably butt splice wires together and can follow instructions, it's achievable without being an electrical engineer. There's tons of good support on this board should you run into problems.
As for cost, affordability is a relative term and might be different for you and me. It will cost you about $200 in parts to rip out the nav system and create new HVAC controls by sourcing used parts, but then you still have to add in a replacement stereo system, and that's where costs can vary widely deepening on what you're trying to do. If you're not going crazy, you can add a good quality Android or CarPlay capable head unit to the factory amp and speakers for around $400 (on top of the $200 for the HVAC controls), or you can go "mid range" and pair the same HU with new speakers and / or a replacement amp for around $1100 ($200 HVAC, $400 HU, $200 amp, $200 speakers (all 4 doors), and maybe another $100 in misc connectors, adaptors, etc. You can aim between the $600 and $1100 by eliminating either the new speakers or aftermarket amp. Whether that's expensive is up to you... the result is a great sound system that makes a 20 yr old car feel more modern, but it could be over 10% of the value of your car.
Look to that nav delete thread for better details, I just wanted to give you a broad overview here.