Just buy 5m (I bought 4 as I'm quite small) of thick cotton jersey. Mine came in 60inch width. Cut lengthways into 3x 20 inch wide strips and ..... VOILA YOU HAVE A HUGABUB! I also sewed a nice offcut square into the front (like the hugabub) so you know where the centre is got tying purposes and it looks nice :-)
My colicky bub is fast asleep in it now and she has screamed every night since she was born. Amazing, and waaay comfier than my Bjorn.