I have a couple of the £40 ones from ebay, but to be honest whilst they do the job, they are not a patch on the Lastolites ones, but at the end of the day, they do a job. I have a cheap double sided white/black which I use a lot as both a background and also as a reflector and light absorber.
i also ordered some of a different make from B&H when the pound was a great deal stronger than it currently is and even with the import duty, vat etc they worked out about the same price as a lastolite one, but they were double sided and very good quality.