OFF TOPIC; not baby related

Wasn’t sure where to post this honestly and I’m incredibly sorry if this isn’t the place.

BUT if anyone could help, I’d appreciate anything!

I’m currently on a budget, so pest control isn’t really an option at the moment. We recently started renting a place and wanting to get rid of roaches completely, inexpensively tho. I know I won’t get rid of them 100% but the less the better, we’ve tried sprays and a paste and it works, but they keep coming back lol. My grandmother in law had always told her grandson and I about a deadly powder that instantly would kill the insects that it came in contact with it., Unfortunately she passed and we forgot the name and have been trying endlessly to find it. It looks like little blue pebbles/sand if anyone can help or suggest something that worked for them? Thank you so much to anyone in advance.