We spend $60,000 to $80,000 a year on signs. I am doing a feasibility study as I already have maintenance people in place and the room. I may or may not decide to do it but I will investigate it as I do with everything I do.
Your post asks specifically about 4x4 coro signs, but your numbers don't add up if you're saying that you spend $70,000 on 180 signs per year. Don't conflate your numbers. You might be spending that much per year, but that includes a lot of other signage you failed to mention.
If you're trying to say you spend that much only on coro, then it comes out to ~$388 per panel. Absolutely no signs shops are charging that much for double-sided 4x4 coro. Check the line items on your invoices.
Want to save money? Talk to your local sign shop or get a few bids. Negotiate with them. 160-180 signs/year isn't a ton of work for most shops, but if you're ordering consistently they'll work with you on price.
If you're trying to do it yourself -- that's barely enough volume to keep your $2k print head from drying up. It will only take you a month to figure out that you bit off more than you can chew, and that buying a sub-par $10-15k printer is just a drop in the bucket compared to all the expenses you will encounter. (guaranteed you'd be trying to resell that printer by the 2nd or 3rd month) And we haven't even talked about labor costs or skillsets. Your so-called "maintenance crew" is going to what... fix plumbing in the morning then switch to graphics design / print production after lunch? Good luck with that. And labor isn't free, regardless of whether or not someone is on salary. Software licenses, controlled environment for materials, employee training, tech support etc.... you have no idea what it takes for a sign/print shop to operate, even at the bare minimum.
Negotiating with your local sign shop is your most cost-effective option. We do what we're good at, meanwhile, you should focus on what makes you the most money -- real estate.
And on a side note... the reason why folks here are pissed about your inquiry isn't because you're trying to save money -- heck, we all want to save money. It's because everyone here has spent many, many years in an industry we're passionate about -- where we invested
many tens to hundreds of thousands on equipment and software that helps us produce quality work at a competitive price. Many years of learning, training, improving techniques etc... it doesn't happen overnight. Asking us to give suggestions on how you can save a few bucks isn't just unreasonable -- it undermines our industry and insults our profession. I won't insult you or cuss you out, but I agree with everyone else's responses.