Go to your charity shop and blow £1.50 on the biggest brimmed ladies wedding hat you can, a 5 inch brim is big enough and black, dark grey or dark brown are the colours I've seen of originals. Unpick any lining and fruit until you are down to the wool felt. If your lucky it will already have a round brim. You can leave the edge raw but its better to bind it with tape. Black or white worsted wool would be best but its hard to come by so a yard or so of cotton tape will do fine.
Get a piece of scrap linen and make a lining, you just need a narrow oblong, sew a tunnel on one long side to take a tape draw string and sew it into place so it looks like this when folded in.
You then need to iron the brim flat, some spray starch helps a lot here. When the brims stiff fold it back and tack each side to the domed part with a couple of big stitches that cross over.
Total cost for that one was under two quid. You can get wool felt hat blanks from a shop in Oldham for 8 quid each, herself got me two and I'm looking for a lump of wood to turn a 8" diameter hat block before I do a couple for myself. Back before the mid 19th c hat blocks were round not oval (head shaped). I think fur felt blanks are about £25 from them.
theres many variations / styles but if you can make one. You can pretty much do them all.
if you need some linen for the lining and tape for the draw cord let us know.
ATB
tom