if you are more interested in building something fitting into the F16 instead of focusing on the one design 4.9,
you can also look for other boats which might offer you a good base to remodel them to F16 spec.

If you want to sail alone, the A-class might offer some good older platforms you can quite easily remodel to 4.9 m by cutting front and rear and which you can strengthen by using the weight reserve coming with it.

a A-cat hull weights nowadays around 13-17 kg, the taipan 4.9 hulls around 22 kg... so you might can even look for heavier hulls and reduce weight in the beams and equipment...

but building complete new hulls is mostly a time eating process like wouter pointed out...

the real costs are surely in the equipment if you can't profit from 2nd hand stuff...

hope this helps and good luck!