Why not fit a TZ250 or Honda RS250 fairing?
Can pick up a nice new one for under £130 and take it to your local engineer, who i'm sure won't charge you £570 to weld a couple of brackets to your frame.
On the seat padding, I've found a roll mat thingy from Millets to be as good as anything 'purpose' built for bike seats. It's about £5 for a roll mat, and there is shed loads of it.
...and when you crash, which you will... I bet a £130 bit of plastic is more appealing than a £400 piece of plastic.
Just my 2 penneth
This was the Desmo Due forum and not the MotoGP one wasn't it?