My Cloud Stream account is free for 2 days of storage. I took a look at the stats, and the number of plates per month average 3700, and this on a quiet residential street.
One of the problems I have with OpenALPR is the recurring recording of a parked plate; a car enters the street triggering the motion event, and OpenALPR tags the truck's plate parked down the street, or a shadow or a cat strolls, any motion event can cause the parked plate to record. Their help forum didn't help much, but it is a free service.