Building an Acat is an excersize in choices.

Having done it myself, one of the considerations in making a 75kg boat is resale. If you build a 75kg boat, you will be able to resell it more easily and at a higher price than a 90kg boat. A used 90kg boat isnt going to be worth much, and since a new imported Acat can be $25 plus, its worth it to think about selling it later.

The majority of the "cost" is in labor. It takes a significant amount of time to make a set of hulls, beam them up/ rig the mast/ rig the boom, mount pintles, fit daggers to trunks, add systems for the tramp, etc.

So, if you are acting on this principle of making a 75kg boat to potentially resell it later, (and you should) and considering your time as valuable (and you should) you would want a light stiff hull. Carbon in the hulls produces a very stiff boat, I wouldnt bother with a glass boat to save money. The choices then are epoxy vs poly vs vinyl. And what core material do you use? Balsa, Nomex and foam are the most popular choices. Each has its advantages/disadvantages. I like Foam, but its a pain to get into a mold. It would work well for a strip plank build. Nomex is expensive, light, stiff, easy to work with but the open cells can absorb water, and can print through on the gel coat. Balsa is cheaper, easy to work with, can absorb water, and rot. I went with Epoxy, carbon, corecell foam sandwich, painted.

Masts. To have a competitive boat, you will need a carbon mast, and a newer sail. No real choice here. Its the engine, you wouldnt want to skimp here

Booms, tiller arms, extensions can all be either carbon or aluminum.

I ended up spending about $12k for my boat. Hall mast, new sail, new tramp, foam/carbon/epoxy/painted hulls, Forte beams, boom, tiller ext/connector, carbon rudders/rudderheads from Aus, curved travelor, midsheet boom, internal downhaul, alum rotator.

I didnt do anything tricky with adjustable diamonds, or adjustable spreaders or special sytems to pop up the rudders or daggerboards.

I know John is saying he spend $8600, but I would bet that once you add every last penny you spend on expoxy, hardware, building supplies, rigging, etc you would be closer to $10k.

Bill