Pearsalls, (yes Pearsall Silks) has 30cm by 30cm (um, 12" square) pieces of Dupion Silk for 2 pounds.

I've not seen it 'in the flesh', so's to speak - just found the page yesterday.

http://www.pearsallsembroidery.com/index.php?cPath=57_60&osCsid=cd0f743d254d968fc971c32b210934d8

Shipping is

Prices for UK delivery are:
Up to 150g: £1.75
Up to 500g: £3.00
Up to 1kg: £5.20
Up to 2kg: £8.50

Prices for EU member country delivery are:
Up to 150g: £3.75
Up to 500g: £6.00
Up to 1kg: £9.20
Up to 2kg: £15.50

Prices for delivery to countries in the rest of the world are:
Up to 150g: £5.00 ($US8)
Up to 500g: £9.00
Up to 1kg: £15.00
Up to 2kg: £25.00

You'd be able to get several pieces in 150g. (They'd know how many).

They have a nice range of colours. 12" is a good size - they do have larger sizes as well.

I can see myself having a Pearsalls Silk Dupion splurge at some point......(as well as my Silk wrapped Purl, and Rennaissance Threads, and French Wired Ribbons and Silk Mill silk splurges).