Scarecrow,
As your an F18 sailor I'm not sure what you are asking as
there is both an F16 and F18 design. I've not decided if I will sell F18 plans.
I'll make that decision once the F18 is in full production.
So I'll just talk in general terms for people who can source F16 and F18 plans from others.

You would build an F16 platform for around $2000 or less and an F18 platform for $3000.
This depends a lot on how you source materials and how careful you are.

Instead of a mould and foam the F18 uses the ply as a self shaping core when it is tortured.
A glass laminate is aplied to both sides. This yields a hull twice as heavy as the F16.
While this produces an incredibley strong an stiff platform the added materials bump up the building cost compared to the F16.

The very nature of the F16 and F18 class means the fitout on both vary so much you really need to decide on your personal prefernces and then price them.

Building is only for those who want to build. If you want to save money get a part time job and buy your platform.
Given the time it takes to build this would be the better financial option.

In my opinion the AHPC superwing is currently the best available aluminium section on the market.
They offerred its use to the F16 class so the Blade F16 uses the Superwing.

Alternatively anyone sailing one up can do what Gary Maskiell did on Altered and source a carbon A class section.
Install a centre web which will bring it up to the min tip weight of the F16 class and have a bullet proof carbon mast for one up spinaker sailing.

I hope this gives a bit of a general idea.

Regards,
Phill