Plushie commissions are expensive, but I don't know of companies that do custom plushies for any cheaper. A company you would also probably have to order in bulk to turn a profit, like most company orders for art related things I have worked with.
I'm not sure how cost effective it would be, unless you have a high-demand. It might be better to give sewing yourself a go, hah. If you're planning on selling you'd might have to order through a company, I don't know if commission artists would be happy with you planning on mass-reselling their work, unless you make some kind of agreement.
This plush company is awesome for their designs but expensive https://www.budsies.com/