Most tires of the same type are very close in weight when new. Probably within 1 or 2 lbs or so. Just figure on around 20-22 lbs per tire, unless you're into race tires, in which case the Hoosiers seem to be the lightest. I would choose tires based on intended use, and performance, with weight only a minor issue unless somebody is really outside the norm.
Check out this Miata
tire weight database The sizes in the table run small for us, but good for relative comparison. Also has links to Bridgstone, Dunlop, and Firestone websites that catalog weight for every tire and size they sell. Also has links to at least two other wheel weight databases, including the best I've seen to date.
In my estimation, you will "gain it back in the tires" no matter what you do. Shave weight where you can. Drive off the rest.
BTW, my RE 930s are about 6 lbs lighter after 30k.
