In my experience, Raspberry Pis are nice hobbyist toys but tend to corrupt data on their SD cards at random and generally are unreliable. For 50k you could at least send them a somewhat rugged fanless PC with a SSD raid for added reliability.
Off-topic, but I've become something of an unintentional expert on making Pis reliable.
First, consider using f2fs instead of ext4 with a nice big card (and get a good one).
Next, attempt to disable all of the unnecessary logging and writes to the SD. Either send them to a server, write them to a ramdisk or even consider mounting the partition in read-only mode. This will drastically increase your duty cycle.
Finally, follow proper system shutdown procedures.
Do all of that (bonus points for putting heatsinks on your chips) and the Pi becomes rock-solid or something like it. Hint: it's not the Pi that fails, it's the SD card.
I will also comment on the SD card quality issue: STOP BUYING SHITTY LOW GRADE SD CARDS AND EXPECT TO BE ABLE TO WRITE TO THEM FREQUENTLY.
Just stop. There is a reason why companies like GoPro (which abusively write cards to death) bless only certain products (the top of their list being modern generations of Sandisk Extreme and Extreme Plus, Samsung Pro and Pro Plus, and Lexar Pro).
In this case, they also make industrial SDs that survive unusually high and low temperatures, which given the nature of this specific context, is worth looking into (although expensive and of low capacity).
I was just recently talking to someone who was very upset that their super cheap 32 GB card wasn't 32 GB and overwrote everything on the card when it ran out of actual space, wiping a whole heap of awesome GoPro footage and photos.
I've had a couple of cards like that before, but after reading an article about fake SD cards a while ago, I test every new SD card and flash drive I get to make sure it's to advertised capacity so I haven't been stung.
They are pocket sized, "plastic paper" water and dirt proof field notebooks. And a stack of pencils to go with them.
Because really, someone running a two-acre farm in some developing country has enough time to make manual adjustments to the irrigation system, manual notes of minutiae etc. They will be manually going through the fields to pick weeds, inspect crops etc. anyway.
Counter point; I have 3 RPis (an original B, a B+, and a 2) and in 4 years have never had any data corruption. I use the 2 every day running OSMC as my media center and the B+ sees very frequent use in a variety of projects.
