I am not sure they are "crazy" expensive, especially the iPhone 5. From what I am seeing on CL, eBay, and Swappa, they are comparable. And I'd have the assurance of buying from a reputable source with at least a short warranty/return period, and getting all of them at the same time. Could I search and buy for less, sure. But I am more interested at this point in the viability of Gazelle and Verizon as sources.
The iPhone 5 is approximately $280-$320 (depending on storage) and the 5s is about $420-$440. The 5s is approaching full cost of a new unit, so I would likely just go new or go 1 step further and get new 6s (but now I am at about $3,000!).
I am most likely going with the iPhone 5. Again since I have to buy 5 of them, the extra $120-$160/ea is a big premium overall.
Also, buying subsidized is not an option. I want to buy phones outright, be it an iPhone or some other smartphone. Verizon is now offering a great new option for bringing your own phones (just kicked off last week I believe). They used to give you a $10 discount when adding a line to a shared plan (was $40 - $10, net of $30). Now, they are giving $25 credit, so the net of each new phone is just $15. This is allowing me to move 5 family members from their current plan over to my shared plan. They will spend the exact same amount monthly as they currently spend for dumb phones, and I will save about $20/mo on my plan and increase the data pool, so everyone is happy.