I can buy Powerpoint separately. I've never done so but I have had to buy Outlook and Access that way. Individual MS Office components are usually around $200.
In the USA, I tell people to just run over to the nearest office supply superstore to buy the Teachers and Students edition of Office. They stopped checking credentials for purchasing that version some time ago, and it's only $100 with all the "core" MS Office programs in it.
I'd probably give OpenOffice a shot before I paid $200 for Powerpoint. You might miss some clipart, but that's what Google Images is for.