I was horrified recently to find that the stellar chair was $199. and made in China. So...I knocked up one from a few scraps and a little steel step ladder that I have.
I simply cut up a piece of scrap 1 inch ply to fit on top of the third stair tread, then I drilled a 12mm hole on the back of the ply and got an "S" shaped piece of steel rod (the type you get for hanging baskets), hooked it round one of the horizontal bars on the back of the step ladder, and pushed it through the 12mm hole in the ply. Hey presto - I sat on it and it worked. Good stability too. For height adjustment I use a discarded home made wooden chopping board (30mm thick - suitably cut to size ) - and a childs life jacket on top of that for a bit of comfort. Apart from the step ladder (which was I think about $30 from Bunnings) $4 for the steel rod was trhe cost. My wife did not think it would be a good idea to post a picture of the contraption as too many of youse good people might become hysterical with laughter and do yourselves an injury.
Just think of the money you could save though........