If you're going to make a cape (short or full length) out of leather, Tandy is definitely the place to keep an eye on, they seem to have been running monthly specials lately where you can get a whole hide (23-26 square foot average) for dirt cheap. you have to have a membership I believe to get their sale prices. I also know people who have great success sometimes finding finished leather hides for cheap online from sources like ebay.
If you are going to go the pleather route- I would recommend against the marine grade vinyl. Only because it is very stiff, and usually its reverse side has wording or logos printed on it and an unnatural texture (criss crossed reinforcing fibers usually). It costs more, but the headliner pleather is the best stuff to use. It is about 30 bucks a yard usually, but the material is 5 foot wide, comes in a better selection of colors and leather textures, is somewhat stretchy, softer and not stiff, and the reverse side is usually a sueded finish- meaning you don't have to line it and it will look natural. Someone I know did a batman costume and his cape is made out of this vehicle upholstery pleather and it flows wonderfully and looks completely natural. Joann's runs coupons a lot, so if you keep your eye out you can find a 40% off coupon and at 5 foot wide 2 yards can give you a good sized cape.
The thing to remember (and this is just my 2 cents opinion) is sometimes you really should spend that extra 20-30 bucks for a better material. It'll look better, you'll be happier with it, and you won't end up in addition spending the money to replace it you should have just spent in the first place.
If you're going for a fabric cape, never underestimate the power of the Joann's remnant sale table. I've had some luck finding some nice wool or cotton fabrics on sale. I usually look for natural materials with a nice woven appearance as this fits into the Star Wars universe aesthetic. You can also always get a monks cloth or duck cloth in a natural or light color and use RIT dye to change the color.