Commercially manufactured costumes are cheap and plentiful at Halloween. You almost can't buy the fabric for the prices they sell for. At other times of the year costumes can be hard to come by and rental shops can charge a half day's wages or more for a decent rental. Creating costumes from found items is fun, and pirate costumes are fairly simple,since they wear clothing that can be improvised from modern wardrobes with a little imagination.
Trousers and skirts
Cut off a pair of trousers with wide stripes in black and white or grey to just above the ankle on a jagged line. The stripes in pirate costumes come from the fact that so many of them were once convicts and escaped in prison garb. Alternatively, choose a rough fabric in a natural colour such as brown, black or grey. Rolling the cuffs may be preferable if a pair of appropriate and unneeded trousers are not available. Cut a skirt of similar fabric and colour for a female pirate. Be careful not to cut too high with your jagged line.
Apply brightly coloured patches of other fabric cut from an old blanket or bed sheet. Tack them on with a stitch or two, or hot glue them into position to add texture. Cutting ragged gashes in the knees of trousers can also give a distressed look.
Add a wide leather belt or tie a rope or bright coloured scarf around your waist for a sash.
Improvised pirate shirts
Wear a baggy poet style shirt, if available, tucked into the belt or sash tied around the waist. Stick with solid colours like white, red or black.
Roll up the sleeves on a bright, horizontally striped t-shirt as a suitable alternative. Basic colours, such as red, yellow, blue and black, work best. Coordinate the colour with the colour of your sash or other accessories for a cohesive look.
Cut the sleeves and neck out of an old dark grey or black sweatshirt. Cut a V at the neck and poke holes down either side that can be laced up with a shoe lace or piece of clothesline or other light cord. This can be worked over a large white dress shirt to give a tunic effect. Wrap the belt or sash around it.
Accessories and finishing touches
Top your shirt with a vest. Stick to basic colours or stripes for the best effect. Red vests are reminiscent of Disney's "Smee" in the classic "Peter Pan".
Pull on a long dark overcoat to give the appearance of an officer. If they are long enough, roll the sleeves up and sew on a pair of brass buttons or glue on a stripe of gold braid at each wrist. Coffee filters with the bottoms cut out make good shirt cuffs, taped into the ends of your coat sleeves.
Draw on a moustache or beard with brown eyeliner. Wrap your head with a bandana, or wear a long wig to complete the effect. For footwear, leather dress shoes, sandals or boots work best. Go barefoot as an alternative if proper footwear is not available.