Boric acid (borax) is effective given a few days. It's cheap and available from a pharmacist.Lay a thin layer of it where the cockroaches will tread in it.We used that technique in a hospital laboratory I worked in. Trouble was the patient food stores were close by and the cockroaches used to leg it when they, and the food (!), were sprayed with DDT (that worked very well).Another possibility, if their locations are known, is cheap domestic bleach. This won't necessarily kill them but it might cause them to emigrate.I am assuming no domestic pets or very small children are present.
Alan Brainsby ● 6401d