I find the tip is to have a few items that can be worn in a varity of ways…
I own only a few items of clothing for larps but they can often be accessorised enough to make the costumes fit to any genre…
For instance…
An old suit
A few scarves/bits of fabric
A basic white colared shirt
A linen shirt with no pockets (if you can find one)
A pair of black pants
Thats the bulk of my costuming and can probably be picked up for…oh…$50 if you know where to look…and can be used over and over for different games.
Then just collect little things people may be throwing out:
Vests, rings, glasses, hats, jewelery, bags…
Also I find a change in the way people wear their hair can make all the difference to their characters costume and look.
People ridding them self of clothing from their closets also provides a wealth of material for costuming. I pick up interesting items when ever I can and all it takes is a little time and modification to build up a chunk of very cool items that can be mixed and matched.
I find the idea of the “old suit” not so bad infact i have 2 old suits JUST for LARPing in.
For me as long as a small amount of effort is made to make it look decent… I dont care where they get it from