FCP was never $3000. Final Cut Studio 2 cost $1200. And this is the case with ANY software, not just Apple. If you rely on old applications, you need to keep using older machines running older OS versions. If you get a brand new computer with brand new OS, be prepared for your old apps not to work....99% of the time, they won't. Especially apps that are over 8 years old.
There are other alternatives to FCX. Adobe Premiere Pro CC is what many dub "the FCP 8 we always wanted." And that can be had for a cheap monthly payment. And has a huge user base, and will keep getting updated.