You didn't mention you were in MA. We have a great used car lemon law in this state. A couple of my keyless go door handles didn't work and I made the dealer fix it under the 60 day lemon law. If he didn't, I was just going to buy the handle myself and DIY in about a half hour, about $175 online, $300 at the dealer, about $500 installed at the dealer. Basically anything that affects use and safety is covered, but not cosmetic issues. So if the trunk closer is broken, then they have to fix it. Had to take it to the general manager before they would agree to repair it, used car manager wouldn't pay for it.
As for C3/C4, it's really the Mux that's the expensive part. The software is out there, you can even find it on some torrent sites for free, but if you had to buy it, they have it on HDD for around $100. The key is that you sometimes need a little support to get it going the first time, something about running a key generator. They usually just remote into the laptop to fix it. That's why buying from a US board member that offers some support might be worth it as you might get some advice on how to actually use the system if you get stuck.
As for C3/C4, it's really the Mux that's the expensive part. The software is out there, you can even find it on some torrent sites for free, but if you had to buy it, they have it on HDD for around $100. The key is that you sometimes need a little support to get it going the first time, something about running a key generator. They usually just remote into the laptop to fix it. That's why buying from a US board member that offers some support might be worth it as you might get some advice on how to actually use the system if you get stuck.