I realize that this post took a turn towards drones, but in the interest of Farm Local v. Farm Outsource I have to say this:
I am lucky enough to work for a company that has over 100 nodes overnight. We have 80-ish during business hours too. It's as dreamy as you would imagine. We are a fully rendering studio though and we complete over 50 animations a year as well as many, many different VRs and Stills.
What I have to offer to the conversation is that Rome wasn't built in a day. We started years before me and small and have added over time. We upgrade workstations (which are not as buff as they could be to save on cost) every few years and add to our farm every few years. Local doesn't need to be so crazy when you can check in the farm. When very large projects come in we buy more machines, maybe 5 or 10. When very, very large projects come in, ones that would take down any farm, we budget new machines in the contract to better the schedule. This is rare, but fits for some clients when you say you can have it on 2-3 months v. 6-8 over their render requirement (4k films are a beast!).
I know I am a lucky artist and I know that my situation is rare, but building a farm a little bit here or there is a great way to go. Get good stuff at first and upgrade memory over time. CPU's can last a while if you start high.
The one cost that you MUST have if you are building a farm though, is an IT Manager. Ours is invaluable on many levels, but when it comes to our large farm, I could not imagine having to wrangle that as well.
You cannot forget the cost of managing, Cooling, Housing, and Electrifying a farm when looking at the cost of it. I would imagine that I could make a few more dollars annually were it not for this, but I don't know that I would make that trade having it.