who are the vendors of LAAS? (I presume any WAAS capable GPS can also
take advantage of LAAS---right?) what are the cost factors of LAAS?


LAAS is nowhere near certification. LAAS approaches are not available.
You'll need a ground station broadcasting GPS correction signals in the
vicinity of the airports. But I wonder what you would need it for if you
get something almost as good as an ILS with WAAS.

--
Thomas Borchert (EDDH)