Disappointed in the lack of consumer advocacy here folks.

Per OP, reservation was made well in advance of picking up the car. Receives a call prior to the start of the reservation they can no longer honor the reservation both parties agreed to.

And we want the OP to walk away and say, "hey Avis, shux, that sure was nice of you to tell me in advance," then pay double the price at a different car rental agency?

NO

If we stand for this, Avis can start routinely overbooking with the intent to never have enough cars for customers and simply call those with the cheapest rentals to say, "sorry, very sorry...overbooked."

I don't know what consumer protections there are in this scenario, but I would investigate. Independent of this, it is important people know Avis made no alternate accommodation for you despite your good faith booking.