as far as i know all kitchen aid stand mixers come with a dough hook and are more than capable of kneading dough.
i have one similar to this and it works fine even for whole wheat dough, which is very difficult to knead.
this one is $189 new and the shipping is probably free
there are plenty of kitchenaids out there for way less than $500
read the reviews farther down the page
and if you are willing to get a used one you can probably go less than $100