Check out Airstar's website, specifically http://airstar-light.us/film_lighting.html and download the Film & TV Catalog; pictures of the balloon lights are in there along with photometric readouts. The 4.8K HMI at 50' high & 50' away foot candles come in at 5,11.
As far as wind goes, the elliptical 4.8K is pretty resilient in the wind as I've operated this in 22 mph winds at the Atlanta Speedway - down drafts are another story. Get a good tech that knows what they're doing.
Helium pricing does vary in different parts of the U.S. check with Airstar to see if they have any connections in area.