Trying this post again - will there ever be a solution to the infuriating problem some of us have of the site freezing when we click reply, losing the post we've just carefully typed???!
I've used Ikea plain fabrics as backings on 2 or 3 quilts. They're slightly thicker than most quilting fabric, but worked well enough. I've tried black and red, and have had no problems with the colours running. The one thing I'd caution against is using them as binding as well - hand sewing through the layers of this fabric was NOT fun.
Last time I was in Ikea, they had a new range of very pretty florals and spots, which I thought seemed to be comparable to quilting fabric. I didn't need any at the time, but intend to give them a try.
It's also useful that Ikea fabric is about 60in wide, meaning it can sometimes be used as a backing without having to piece it. And the prices, especially for those of us in the UK, paying a lot for quilting fabric, are great.
And on a different note, Leah Day recently pointed out that Ikea do a very inexpensive range of very slick table tops for which you can buy adjustable legs, so perfect for a quilting set-up.