With regards to the ideal crew weight a note:
at the Newport Regatta, held in medium to light winds, races were won by crews weighting 300, 350 and 380 lbs.

With regard to the entry cost have a look at the classified on the US 18HT web site:
you will see that you can buy a very good used 18HT for less than 9,000 USD.
I doubt that you can find a very good used F18 in the US for the same amount of money!

With regard to the quotation of new boats, I am aware that in Europe a Tiger, a Cirrus, a Mattia etc., when you add all the racing optionals, is priced well above EUR 15,000.
For a new Javelin 2 you have to pay only EUR 12,800 and for a standard Stealth 18HT EUR 12,000, i.e. some 2,700/3700 USD less.

Moreover it is true that the 18HTs have far less fittings than a F18, but it has to be underlined too that they features an expensive carbon mast and hulls some 10-14 Kg lighter than the ones of a F18