Hi badvegan,
The better options I’m aware of in the San Francisco / Oakland area are listed in post #2 here. I don’t have a list of specific mattresses or prices for each of them (other than what is on their sites) to see if they carry a mattress that would match your specific criteria so you may need to make a few phone calls to ask them what they have available in your budget range that also meets your criteria.
If you are comfortable with CertiPur certification as far as toxic offgassing then a traditional innerspring/polyurethane mattress with US made or CertiPur certified polyfoam would be a good option. I would make sure that the polyfoam was at least 1.5 lbs density for a two sided mattress and 1.8 lbs for a one sided mattress.
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You may find a latex hybrid with a polyfoam support core and a latex comfort layer in your budget range.
A few online options that are inside your budget and may be worth considering from some of the online members of the site include …
https://www.sleepez.com/latex-mattress-sale.htm (6" of natural Dunlop latex with an inherent rayon/silica fire barrier).
Twin Solid Core Latex Mattress Only, Solid Core 7" Latex Foam Mattress, Latex Mattresses-Talalay and Dunlop, All Products (5.5" of blended Talalay latex with a wool fire barrier)
https://www.amazon.com/Ultimate-Dreams-Latex-Mattress-Queen/dp/B0051AQXZK
https://www.amazon.com/Ultimate-Dreams-Natural-Latex-Mattress/dp/B008E0LZLG/ref=sr_1_13?s=home-garden&ie=UTF8&qid=1371712846&sr=1-13
All of these last 3 are latex/polyfoam hybrid mattresses that have 3" of latex and a polyurethane quilting layer over a polyurethane support core. The Natural latex mattress uses Dunlop for the comfort layer and wool for the fire barrier and I believe that the other two use an inherent fire barrier as well but I don’t know the specific details.
Innerspring with chemical free natural wool and organic cotton comfort layers.
Between some of the local and online options you have some very good choices available to you that are inside your budget range.
Phoenix