Star with any eastern style shirt of your choice. You should be able to grab something online for around 30 bucks, likely much cheaper with more digging. I just know off hand where to get a chinese shirt with a mandarin collar for that much. lol You can go mandarin, cavalry, gi, whatever the russian one is, or anything that gives you the feel. I've heard of people starting with medical scrubs before. Color is your choice, of course, but browns and grays would reflect the gray status you said you were going for.
I'd not think about a cloak for now... as I don't know where to get one on the cheap that will look good in a well lit area. Pants are pretty simple, and also can be had for 30 bucks and under online. I suggest any kind of martial arts pants, and go for a material like linen that has a nice natural look to it. Pick a color that's the same as your shirt, but a different shade so there's some layering to your look.
From there, get boots of your choice. Real high quality boots are pricey, but I know I've heard of some nice looking pleathers and such out there in that same 30 dollar price bracket. A belt can be made for that price as well by hitting your local Target or Wal Mart. Just get a plain black belt with a squarish buckle and either paint over or file off any text or logos on the buckle. Then suck it up and walk over to the women's belt section and pick out a nice match from those weird super thick fashion belts. Wear the regular one over the huge one and you have an instant Jedi belt. Pouches should be leather and can be picked up either at the con out of your spending fund, or from local army surplus or thrift stores. Knife cases work great as well, or you can get a spacey looking box and superglue some clips to the back to attach that as a pouch. You can also grab a covertec for your belt from US here for about 11 bucks. Even if you don't use it at the con, it looks real good on your belt while you carry the saber.
The last thing that will leave you is something to help layer your shirt more. You could try looking for some sort of old style vest like from a pirate movie, something long that would hang out from beneath your belt, or else you can pick up some cloth from someplace and throw together some tabbards if you have a friend who can do basic sewing. You could also throw together some cheapo-deluxe armor from foam or plastic and a little paint if you are creative enough and can lay your hands on a little of the stuff.
Hope that helps!
