|Based on image by woody1778a|
Pennsylvania has a budget of almost $4 billion. 14k automated license plate recognition(ALPR) devices would have an initial upfront cost of at most $100 million. To maintain the system would cost about $15 million if all the system did was log data, alert police about problems tags and allow ad-hoc searches. I'm basing all this on the cost of systems with many fewer ALPR devices so the cost should be lower given the volume being purchased. In addition, the other systems do much more such as issue speeding tickets and running red lights among other things. I'm calling it a wash on yearly costs because of the greatly increased amount of data balanced out by it being much less complex since it would not issue tickets.
One of the more difficult problems with these systems, especially in the US, is they have to quickly account for changes if a state adds more characters to their tag or changes the type of font used. To track out of state traffic requires that the system keep up to date with a the tag changes from at least the contiguous 48 states. Also when a tag is scanned there is no way to tell which state the tag belongs to because the numbers are repeated from state to state. From what I've read, when a tag is flagged as a potential issue, such as stolen, a person must manually verify that the tag is the correct state.
These issues along with potential public outrage are probably the only reasons a state hasn't decided to institute a system like this state wide. Public outrage has been ignored for a long time in many other areas by politicians so I believe it's the combination of the technical and political hurdles holding everything back. The time of ALPR will be near when a state institutes a QR code like graphic that is both easier for a computer to read and also contains additional meta data such as state, VIN, car color and make in addition to the tag number.
It's just a matter of time.
Update: A story from the Boston Herald about Massachusetts gong to storing all the plates they scan when driving around.