It's definitely an ambition of mine to own all my own equipment so I can train in the privacy of my own home some day. So far the bare necessities on my list are:
A pullup bar
a squat rack
incline and flat bench (or adjustable)
An adequate set of dumbbells - in the range of 30kg - 70kg perhaps. Not too sure how much a full set of dumbbells (ala a dumbbell rack) would cost, but I am assuming thousands of pounds/dollars
A cable setup (possibly intergrated into the squat rack, bench etc. I've seen a few of these floating around)
A leg extension, and POSSIBLY a leg press setup
And obviously a bar and weights
A cable setup (single cable setup, double is not necessary since I don't really do cable flies)
For cardio, a small treadmill will be fine.
I'm probably missing a few more, but those are the main things I would definitely love to invest in in the not too distant future hopefully.
Here's a nice setup I came across (not everything is visible, but it looks really good). Just use imagination to picture the bench on the left lol: