I think as far as the Dumbell angle, one could get by as follows:
A good set of Olympic collared dumbells (or 2 sets).
At least 8 10lb plates and 8 5lb plates.
Also 4 2.5 lb plates.
Here you have good stable dumbells to 70 or 80 lbs. Even with 2 10's and a 5 on each side good Olympic collared dumbells are still stable and compact in width, though a little long because of the length. Easy to change too. And if you have 2 sets, I am sure investing in another 4 10lb plates and 4 5lb plates wouldn't put you back more than 40 bucks.
Secondly Buy a set of 50s, a set of 80s, a set of 100s and a set of 120s (if needed). Here you could probably get in for 60 cents a pound per dumbell so around 400.
Also pick up two sets of 5lb magnets, one for each end, and 2 sets of 2.5 lb magnets. This will make the 80's to 90's, etc (or 85's). These are made for dumbells.