Did you want the solid more Victorian
in which case buy a LARGE felt blank from tom norbury and some shellac dissolved in meths (craft shops do felt stiffener) and you could do it yourself, just steam and block the crown stiffen the whole thing put braid on steam and shape the 'leaves' stitch into place, o and sew a band around inside the crown to stop the felt expanding when you sweat. Or order one from Kittyhats, pay her do all the hard work.
But if you mean the folding chapeau bras style?
Thats a whole different kettle of fish as it's a complicated stitched woollen folding envelope cap(like a WWII side cap) inside a buckram oval covered on both sides with felt/wool then trimmed and is a beeeatch to make hence the cost.
You could get a side cap from a WWII supplier (like these http://www.militariaonline.com/shop/index.php?main_page=index&cPath=19_9_50&zenid=5d976aafbe4a44fcb35c31b07e6975cb
) and use that as the base , remember not to sew the oval at the front and back or it won't fold flat, buckram you can get from places like John Lewis, braid from hand and Lock http://www.handembroideryshop.co.uk/acatalog/TRIMMINGS.html
and some nice black melton from Bernie T Bolt or Hainsworth and lots of sewing.....good luck.