Can't help you buying commercial models. But I strongly recommend making one you could probably have 3 or more for that price with a bit of scrounging for old computers especially external hard drives. I think there's a thread something like '$20 stir plate' or even a newer refined post of the original. full instructions with photos. Most expensive part is the stir bars.
But if your real lazy I could make you one for $80
for that price you have to build it yourself...mine went like this
240v 80 or 120cm case fan - jaycar
ceiling fan controller - buggins
box to mount it in - jaycar
big zinc washer that gets glued to the fan - local hardware
2 x neo magnets - aussiemagnets
stirbars - auscrown
i have not glued the magnets to the washer in case i want to doodle around with the spacing for different sized stirbars