wow $600.. i think would be much easier to take it to a tailor anywhere, maybe in the markets and ask them to measure and make a cover.
we're lucky that my mom tailor made and sew all our covers for the baby, from v-shaped pillows to custom-made covers for high chairs. i don't think it's that difficult if you know a bit of sewing. it's quite crude, but works. maybe you even want to take a shot at it if interested.