Tweed or tartan? probably your preference or your kiltmaker's preference. I think it'd be easier for me to work with the tartan (if there aren't too many stripes).

For a 4 yard box-pleat, consider shopping Scotweb for 2 yards of (double width) Marton Mills Jura (16 oz). That's quite affordable, especially with the current exchange rate; it's easily under 2 kg, so it can ship Royal Mail/USPS if you choose. Stick with 16 oz for the box pleat, per advice from the professionals.

If you want to go for an 8-yard, watch for deals. Perhaps our friend CLANTARTANPLAID will return to his Ebay store soon. Check the remnants at Fraser and Kirkbright or the Scottish Weaver. Try to get 13 ounce or heavier, though F&K's 12 ounce is promising & also available at Scottish Weaver BTW.

I made a "practice kilt" from a fabric store remnant, mostly polyester with a bit of wool. This is NOT recommended by the pro's, but it helped build my confidence. I had to re-learn how it felt to sew the pleats on real tartan, of course. Then I lucked into some nice fabric in appropriate tartans from Ebay sellers at about half-price.