Have you done a search for Bird-Cages on your local Craigslist? If not, then I HIGHLY-SUGGEST that you do that first, BEFORE you even think about buying a brand-new Bird-Cage, and I only say this because you will be able to get your Umbrella Cockatoo the "Taj Mahal" of Bird-Cages for $500-$600 if you buy a pre-owned one!!! You can usually even find pre-owned Stainless-Steel cages for that budget on Craigslist that have a new MSRP of $2,000 and up! I'm not a huge fan of the Stainless-Steel cages, not because they aren't totally awesome cages, because they definitely are, but rather because I'd rather buy my birds the largest, nicest, most decked-out cage that I can for the money I have to spend, and for what a brand-new, size Medium to Large Stainless-Steel Bird-Cage costs, you could build your Parrot it's own wing on the house!!!
Seriously though, I highly recommend that you jump onto your local Craigslist page, go to the "Homepage" for your town/city, and then look under the "Community" heading, find "Pets" under the heading, and click on "Pets". That will take you to your local Craigslist page where all of the Pet supplies/equipment/food are sold. Then you want to find the "Search-Bar" at the top-center of the Pets page, and type "Bird Cage" into the search-bar. Then before you do the search, go to the left-side of the page where it says "Search Distance" or something similar, and you want to set the distance from your town that you are willing to drive to pick-up a cage...Craigslist allows a maximum search-distance of 200-miles, and I always do the 200-miles search-distance just so I don't miss anything that might be worth the longer drive. (some people's small towns/villages don't have their own the closest town/city to where you live that has a Craigslist page, if your town doesn't have one)..
The private Avian/Reptile Rescue I have been with for over 8 years now is not a non-profit or 501c3, so we get no monetary help from the government, as it's owned by a couple in their 50's, with the wife actually being the Director of the Rescue and the person who runs the place (and does it well I might add)..We do get lots and lots of donations from the local communities around us, and we have a wholesale-deal for food with Higgins, Zupreem, and Kaytee...But when it comes ot both Bird-Cages and Reptile enclosures/vivariums, as well as Reptile lighting/fixtures, we are constantly, every day searching for good-condition, pre-owned, and our #1 source is Craiglist by-far...There are usually dozens and dozens and dozens of pre-owned AND NEVER-USED PRE-OWNED large/extra-large Bird-Cages for sale on Craigslist at any given time, the reason being that #1 Large Bird-Cages take up a lot of space and people don't want to store them if they're not being used, they just want them gone, #2 People don't want to look at an empty Cage that once held their long-time baby who is no longer with them, and #3 People pay a lot of money for large Bird-Cages when they buy them brand-new, and even though they know they are going to lose most of the money they spent on the Cage originally, they want to get back as much of their money as they can, and they know that the sooner they sell their Cages the more money they'll get for them.
And there is nothing at all wrong with buying your Umbrella Cockatoo a pre-owned Cage, they pose no dangers or health-risks to your bird as long as you fully-disinfect the Cage with either F10SC or White-Vinegar and hot-water before you put your U2 in it, Pre-Owned large Bird-Cages are absolutely the only way to go, especially for a parrots/birds who need a ton of space inside of their Cages, not only for them to be able to move around, flap/extend their wings fully, have lots of room to climb, swing, etc., but also so that you can put lots and lots of different types of Toys, Foraging-Activities, different types of Perches (including Rope-Perches, Cement/Nail-Trimming Perches, Natural-Branches you find outside and bake, etc.), along with a large swing for him, etc. And again, if you are planning on spending $500-$600 on your bird's new cage, if you go with a Pre-Owned Cage you are going to get a TON OF CAGE, versus what you will get for $500-$600 if you buy a brand-new cage that has to be a large/extra-large size; basically you're going to get very little for a size large, brand-new Bird-Cage wise, typically sacrificing in the quality of the cage when you have to buy one large enough for a U2.
I'd jump onto Craigslist, do the search in the "Community-Pets" section of your local Craigslist and make sure that you extend the search out at least 100-miles, 200-miles would be better just so you see what's out there right now, and then "Bookmark" the pages of the ones you like, and the come back here and either post the links to the cages you're looking at, or simply save a photo of each cage you're interested in and then post the photos here so we can see them and then give our opinions of them. That's the way you are going to get your U2 a TON OF CAGE that he'll love and have lots of room for his stuff and for him, and at the same time you'll be able to stay WELL WITHIN OR UNDER YOUR BUDGET, as opposed to what you are going to get if you look at brand-new bird-cages that are large enough for a U2, which will be very, very little and probably low-quality as well for that budget-range (which is ridiculous, I know, they are stupidly expensive brand-new, which is why I always buy a pre-owned one for my own family as well as for the Rescue)...