I would wait to buy donuts until they go on sale, which is usually at Christmas. Or at least wait until they bring out the Black Friday deal and see if there's something you really want. They also have sales on items during Christmas, so I'm waiting until either Black Friday or Christmas to buy stuff. If you don't want a limited time item, there's no reason why you can't save a few bucks and wait a month to get it, right? :)
Personally, I have 1766 donuts saved up (I bought some for my birthday in June but was really stingy with them, and I also grinded (ground?) like crazy during Endless Bob). I'm going to go nuts during the sales!
And yes, Powell Motors is a good choice. My Springfield Heights wouldn't feel complete without it. :)