A lot of people discover this when they try to build a custom bicycle from the frame up with off-the-shelf components.

Similarly, if you want to build your own furniture, you'll find that Ikea furniture shipped overseas is cheaper even than wood bought locally!

You could probably build a decent chair with a saw and an axe and a tree if you had to. It may not be very comfortable or sturdy and if you didn't allow the wood to dry first it would probably break in a matter of months just from the wood shrinking as it dried, but if you had to you could do it.

I wouldn't need to build furniture with an axe because I have a decent woodworking shop in my garage.

However, what I'm saying is that your cost for just the tree (for the raw material) is greater than the cost of pre-made manufactured and even imported-from-Europe furniture. So you can't save money with DIY furniture building.

My father built a large sturdy shelf unit from reclaimed planks he sourced from left over ammo crates after the war. It can be done cheaply if you are concerned about functionality more than looks. Get some lumber and wood paint. First, you don't care about weight, easy assembly process and shipping costs, so you can use heavier materials, proper metal screws, profiles, brackets, etc. But you do need some tools, like a drill, jigsaw/circular, etc.

That's just bad accounting. "Reclaimed planks" aren't free materials any more than something I bought last week for $100 is free today. There's something called "opportunity cost." Someone who uses up $100 worth of reclaimed planks is spending $100.

Under the Iron Curtain it was quite popular to build whole car out of spare parts in the seventies up to early eighties due to rationing. It was significantly cheaper too.