Repeating a previous post:
Personal favorite in Recoleta:
https://maps.app.goo.gl/PgmPZrs6vSLp6jpz9 Azcuenaga 1193 - GIRARG Money Transfer. Like other businesses (Pago Facil etc.) pays sufficiently close to the blue rate that you will probably not want to bother searching out a cueva. Safe street, safe place. The main trick is to find a location close enough to you for convenient transactions.
Note this is a frequent topic in this group and a search on terms such as cueva or currency exchange, etc. will provide more than you care to know.