how much is it purchase a p.o. box?

$60 ish for the smallest per year rental. You may be able to get an extra month with a new application. The rates differ between the stations. I think only main office on Chapman has a 24hr lobby, some offices lock the doors for the overnight so check before you rent. Current ID, proof of your residence ( elec bill, rent/mortg agree.) you don't have to live in the same city. Each adult you want to recvd mail at the po box must be present with ID or docs that give you auth to manage them ie Power of attny, death cert Check first, application at the office. I think you can download at USPS.com print and bring in person to office. Be sure to check lobby hours and access 24hrs if you need that

About $80 for a year and $40 for six months