Building a boat from the ground up is a lot of work, but not impossible if one just want to do it. But it is probably not something a lot of people "just want to do". As Wouter and John expressed, you dont really save a lot by doing it this way either. Buying a used boat, or fixing a boat somebody has had in their backyard for 10 years is probably the cheapest way to become a boat owner. When we bought our Marstrøm Tornado, we bought it as a co-ownership. It has been very succesful as we both have wanted to sail and race the boat often.

For a cheap F-16 project:
Home build hulls in ply.
Get all deck hardware, crossbeams and rig from a broken cat.
Homebuild foils and ruddersystem.
Design, cut and build your own jibs and mains.
Buy a spi kit pre-cut from a sailmaker and assemble at home.
Learn a ton about your boat, boats in general and sails in the progress and have a unique craft. You can also say "PRRRRRR" in the general direction of the "consumer society".

If one begins estimating how much $$ you would have made by working instead of building on the boat, it is not worth it! You need the right mindset and enjoy the experience to succeed. Finding the right sources of materials also take time, but it is well worth it for later projects.

Assembling is much easier, but again it takes some determination and initative. I dont think the "consumer society" is able to buy into the idea unless there is a certain amount of group thinking and support going on, like what Steve describes from SA.