The Apple I, like a few other machines, is becoming the Honus Wagner baseball card or the Superman #1 comic. The machine has gone well beyond the vintage computing community into the realm of high-dollar collectors.
The $600K investor will probably make his money back fairly quickly.
The sad part about the Altair is that it's a really bad example. The PS is totally redone, the CPU card has a replacement chip, the RAM isn't even MITS, there is no original documentation, etc.
eBay value for that system would be $2K +/-.
Not sure what's up with this site, but if they want to list my Altair it's twice what that machine is, so... :D