Not even close, lots of retro offerings are going to be 6-9" from face, as they are designed to be a 1 to 1 for fluorescents (They really aren't close to the same uniformity as the classic glass tubes, uncertain if they will ever be). If you want to get into other solutions, like Posterbox modules, now you're talking some serious cash. Like gino said, this is probably 4.5 or 6" deep, plus painted embossed pans, makes it 5" from the face. It's probably got T8s on 6" or 8" centers.
Your example, I am honestly surprised it looked fine. I'm going to wager it was a white panel with a print on white translucent, which really helps cut down on light transmission, and therefore less hotspots.
Who did this mess? Why route the electrical right through the roof when you're so close to the eave? Honestly, I think this sign was doomed by the storm from the get go, you're face wouldn't have survived regardless, looks like it ripped part of the cabinet from the support. Also, some jagoff left a 1/2" eyebolt in it. Those are like $12 each...
You should be able to estimate this easily if you have the vaguest of dimensions, as long as they exceed the actual dimensions, your pan face will cost the same or marginally less when it comes to production time. I'd still include a note on the quote, company not responsible for incorrect dimensions provided by customer.
As far as lighting, everyone else is correct, except tex and his 2.5-3" from face comment. Also, a flat panel is probably only going to shave 20% off the materials cost vs a pan, whereas an acm panel could cut it by 50%, but then again with all that drive time both these percentages will be drastically reduced when compared to the whole job.
Now whether or not you want to get into this kind of work is the big question! Go rent a tow behind lift, trim some trees in your yard, generally play around with it, and see if it's something you'd like to do... with 3 people watching you, while holding something expensive.