Darth Maul is one of the cheapest costumes if you are not into perfection.
There realy was an official costume for little money. Of course you can forget about the boots imitation, so I cuttet them off right away. Also the rubber-belt is not the best quality. It will not stay and is way to big. You may find patterns in the internet for this costume and you may get it tailered but this will cost..
Should be black leather gloves.
I suggest black horse-riders boots that may be cheap depending on the quality.
The half-face mask of the official costume was so bad that it only works as wall-decoration. I recommend a rubber mask that sometimes appears sometimes on ebay. Unfortunately the color bleaches very fast on this mask and it looks soon grey and pink. To prevent that, go to the next gas-station and buy some liquid that keeps the tires of your car black and apply a little bit to the mask. I also attached some buttons on the backside of that mask for a better fit. If you are into perfection, shave your head and start painting. Think twice before you get tattoed.
Depending on the money you want to spend, get either a plastic toy-sword or a Masterreplicas made of Aluminium.