Not that difficult? I think we must have different views about difficult, lol. My network rack is on the lower level on the far corner of the house from the mailbox. It would be like a 200 foot run that would I assume have to be buried or well-hidden through a yard and/or driveway... not to mention get fed back into the home again and through walls. Because my mailbox is only like 10-20 feet from where I would want the license plates captured, I figured there was probably a wifi solution that could work reasonably well. Is this really not the case?
There is no (cheap) WiFi solution for LPR that is going to work well, at least if you're relying on WiFi to deliver a real-time stream into your home. You're talking about 20 fps video at 2 MP from what appears to be 50 or 60 feet from your home; it is far too easy for WiFi to be disrupted or drop out at that range. You might get by with a camera that incorporates continuous time onboard SD storage, with the idea of using WiFi to download a selected video clip, but even that may be frustrating if you have to skim through footage to find what you want.
The other issue is one of power budget. A battery powered WiFi camera will
not work for LPR. So if you're going to mount a camera on your mailbox, you'll still need electric wiring to power it. And if you're going to that amount of effort, you might as well run Ethernet cable.
A 200 foot run is not an issue for PoE+ routers. You can buy waterproof cable that can be trenched into the ground with a spade - no conduit will be needed. It's not trivial, but it is certainly workable.
Also, I think I may have confused myself (or maybe I'm still confused) about needing two cameras for license plate reading. I know I said "coming and going" but my intent really was just to capture license plates on the back of cars at the stop sign. Wouldn't one camera suffice for this?
I can promise you that within a month of installing one LPR camera, you'll be installing a second one to capture plates in the opposite direction. All it will take is one "missed" plate, and you'll be kicking yourself for not having the second camera. Of course, if your roadway is a cul-de-sac that forces anyone who drives in to drive out through the same intersection, then you could conceivably get by with one camera, but I'd still recommend a second one. The additional effort and expense of adding the second camera is small compared to the effort and expense of adding the first.