To answer in order....
1. Pretty much anything, cotton, polyester, wool, some are even made from insulated materials, but you don't want that or you'll die.
2. An O.K. suit in a readily available color runs about $10-$15, I suggest a local goodwill or Salvation Army. Also, when googling, use "coveralls" and "jumpsuit" as keywords too, many listings will come up.
3. More than to buy one, unless you are REALLY desperate for the right color, and you have the fabric picked out, don't do it.
4. Unless you are a seamstress, and do this for a living, I wouldn't.
If this helped let me know, if you need more help, contact me or Ladysewforus, or darthcarcinus, both are great fabric workers.