Syntace make a 75mm stem. Claimed weight is 87g w/ ti bolts. And it's under $100US.
I think Supergo sells them for $90, but I don't think they come with the Ti bolts.
Ritchey also makes some great stems. This is the one I have. They go down to 80mm. I think I picked mine up for $30.
With a short stems, I've never noted any flex, but then again, I'm a light weight rider. I don't think 'stiffness' os going to be an issue for you, unless your twice the size of Jan Ulrich.
Good luck, hope you find the stem of your dreams... and you're smart for not comprimizing your bike fit.