What do you mean by some have extras? I only recall there ever being a single invisibility cloak in the entire HP series. Assuming this is correct, I don’t think it’s a valid assumption that just because somebody has a lot of money means they can buy whatever they want. My impression is that the invisibility cloak is incredibly valuable, beyond any price that anyone could offer for it.
It’s a very unique item.
Moody has two, a main one and a spare, but one was taken in the field. Harry has one, and we’re assuming that Dumbledore had one (but that’s just speculation), so there might have been one available for Malfoy (The one Moody lost.)
Death Eaters don’t seem to bother to much with the cloak and daggar stuff. They are very open and public, just look at the Quiddich world cup.
A small group against so many and the good wizards still fled in terror.
Malfoy didn’t need a cloak in Hogwarts either, he was in the room of requirements most of the time with Crabbe and Goyle gaurding outside posing as two girls.
Once Draco knew how to fix it it would have been quick work and he could just as easily used the polyjuice potion. The Malfoy’s may well own an invisibility cloak, but that doesn’t neccessarily mean they use it.
There was no anger when he stood on his face, just maliciousness. You don’t need to be angry to hurt someone, in Malfoy’s case he would have enjoyed it.
That said would he have wanted it if it was Harry’s? He would have been more likely to destroy it than keep it.
I think he didnt take it with him mainly because he wanted to hide Harry so nobody would find him for a while. If he really wanted one, he could afford one easily. Or steal it. Or threaten someone into giving him one.