I have a bag of ground maca in my cupboard. I stopped using it as soon as I was diagnosed. (I hadn't used it for very long before I was diagnosed, so it should have had no impact on my cancer.)
The Macafem tablets contain 500 mg of maca. They do not appear to be standardized (although I'm not sure what they'd standardize for anyway.) That means each bottle of 100 tablets contains 50 grams for $28.95. You can buy a one pound (453.5 grams) bag of maca from Navitas Naturals for less than $20. It's a real pain to mix in smoothies and such, but a little bit of fat (like coconut or olive oil or even a nut butter) goes a long way to make it easier.
With that said, maca stimulates the hormones, so it is not recommended for women who have hormone-dependent breast cancer (see the Macafem faq, here:
http://www.macafem.com/macafem-faq.htm).
Sage is another herb that's reputed to put an end to hot flashes, but the information on how it affects hormones is sketchy, at best. I know that Sarah's "Food for Breast Cancer" site recommends against it:
http://foodforbreastcancer.com/foods/sage
(And I stopped using it for that reason, although I was using it for memory effects, not for hot flashes, which I do not have. Yet.)
There is other research to indicate that the phytoestrogens in sage may not be a problem, but as she says, "there is not much interest in it among breast cancer researchers, so few studies are available."
I will try to post the sage monograph later if I can get the Natural Standard site to behave itself. Also, if I can find anything else that might be a safe and effective alternative, I'll post that too.