I just ordered my first iPad, a refurb iPad2 and starting to research cases that are not too expensive. That Invellop case looks great and I just added it to my Amazon wish list. It might be either that one of just a sleeve like this Belkin as I use a similar Belkin sleeve for my Kindle and love it.
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If you want cheap, then check your local dollar store/5 Below for some neoprene sleeves. Discount retailers like TJ MAXX, Marshall's, etc generally have a lot of old iPad 2 cases lying around for around $10-$15. And, as always, there's eBay/Amazon for a lot of other cases.
I did what h1r0ll3r suggested and just picked up a cheap neoprene sleeve. The one I have doesn't really even fit the pad...slightly large...but it protects it in the rare instances that something might hit it.