I would say in general, I agree with your opinion. But, the price is more then worth after going to look it over today and based on others I see around me and what there asking for them. The mmm is my only need for it and I have time and energy to burn in the process of finding one....LOL
Kenny is right on, on this one! What is the price of the 4100?? That will go a long way to telling us what opinion to have. Yeah steel is up CUT prices are WAY up, but I have been buying/trading/swapping/selling JD CUT's for years, and it is ALWAYS cheaper to get the CUT with what is needed, be it tractor, tractor MMM, or tractor, MMM, loader, or backhoe.
Sure I've pieced together LOTS of tractors, put together lot of things Deere said can't possibly work together, which they will, but I was able to do this because I had pieces from OTHER combos that I took off to install what a customer wanted, AND had local scrap/junk/parts yards semi close to me. That lowers the cost of assembly WAY down! NO spending 700.00 plus to get the correct mounting kit/brackets after the fact of "Got a Super/Great deal"
If this 4100 is mint, low hrs, got it for a song/cheap/a steal, then sure go for it. Been there done that lots of times. But you haven't shown us much about this 4100. Kind of tying our hands here. By the ONE pic you have shared it looks real nice, low hrs. Owner did nice job installing rear lights, and it looks like it is loader ready, meaning it has the loader SCV's, which they ran extensions off of it to the back of the tractor. Kenny is correct no PB, never looks like it had brackets for a backhoe, so no concerns there.
Hey look, an awful lot of my former side job was hitting Dealers for thing they just wanted to get the H*LL off there lots. I still am grabbing things for my 4720 cab, and Gen 2 2032R today, but it takes YEARS to get some things, and a crap load of time scouring EVERYTHING! on the internet/dealers lots, phone calls.
I got lucky, and saw the shift in the CUT market coming, and sold off my CUT inventory, then Covid-19 came and wiped out my stock of parts, AND my supply of parts. No more "I can't pass this up" deals. I did make a lot of money and got a lot of people on here what they needed/looked for, and others, but the decks you are looking at, pre Covid were 3-400.00 dollar decks
You May have found a "can't pass up deal" but be careful, Kenny is right, most times piecing together a "unit" cost way more. I've done it, and been on both sides of the coin. That's the reason I have posted this way too long post.
We here need a LOT more info and mostly pics to really help you out the right way. And yeah, it is fun hunting things down, making things work, the thrill of the deal, art of the deal. You get the idea. I take pride in my area for making things work that JD says won't work. And I've never had to get anything cut at a plasma cutter shop. Got one now though!
Best of luck, good hunting, and get the pics of that 4100 posted. Then we can steer you the right way.
Allen.