A more affordable fabric that that has been used by some costumes is Jet Set Polyester, this fabric is a jersey knit with a tiny bit of stretch, however, if you are looking for a more accurate fabric, other options that might be more affordable would be to get a synthetic crepe de chine.
(Note: crepe de chine is most likely the fabric used for the dress, as the other construction details in Star Wars Costumes: The Original Trilogy seems to check out with what is known about the dress from other sources.)
Devorè velvet, also known as burnout velvet, is used a lot in Padmè’s clothing, and also in many other costumes throughout the prequel trilogy. Devorè velvet us usually made by using a blended fabric such as, silk/rayon. A blended fabric of portion based fibers like silk, and cellulose based fibers like rayon have a mild acid is used to eat away the cellulose threads leaving a shire cut out panel.
Moire fabric is likely the kind of fabric used in the body of the gown of Padmè’s deleted scene senatorial gown from (Attack of the Clones). Moire fabric is sometimes called watered silk and historically Moire was made into silk taffeta and now is made into other, sometimes synthetic, fabrics. For Padmè’s senatorial gown it’s likely to assume that it is made out of Moire silk taffeta, in gold.
Jo-anna’s Fabric’s has a cotton/polyester blend available online; the fabric can be purchased at other sites online as well. (Note: that cotton/polly will be hard to dye gold, an all natural fiber, or a synthetic in gold, would work best.)