I think perhaps a BETTER solution in your situation would be to get your mother a lovely statue or perhaps art print of a cockatoo, not a living, breathing bird.
The cost of the bird itself is cheap compared to the upkeep costs of them! And I'm unsure where you live in the world, but unless you are buying an older bird off craigslist or something, no where in the US/UK/AU etc... will you be able to find any species of cockatoo (besides a cockatiel) for under $1000. Cage for a cockatoo will probably cost $400 in and of itself (if not more, they need a lot of room), in addition to another couple hundred on initial perches, toys, food etc... and figure with cockatoos being big time toy destroyers, probably $50-$100 PER MONTH on toys. Can your mother afford that? And what if the bird gets sick? My bird got sick and the FIRST vet visit was $350, and he needs to go back a second time to confirm the infection has cleared, which will be another $300 or so dollars. Think this through! If you can't even scrape $400 together, a large parrot is probably a bad call unless your parents can afford it, in which case it should be THEIR choice to buy one.