Need a Recommendation for a Roach Exterminator

I have a ten unit building in PS. There is no infestation but a hugh roach is popping up fairly frequently. Two tenants have complained, and one is phobic about it. Threatening to move out if something is not done “immediately”. I see one in the basement sometimes.
Is an exterminator a one time thing or does he have to come on a regular basis?
How much does it cost?
Any recs?