Coqui, I strongly recommend following Dr Gross' recommendations about Fosamax for the next six months (assuming that's why you're looking into this). It prevents bone resorption that happens after the surgery, and if you're starting with low bone density then this resorption can let the bone density get dangerously low risking a femoral neck fracture. Initially I really didn't want to take it but I think it makes a lot of sense as short-term risk mitigation.
I'm in the same situation (my operated hip was in his middle ground where I don't have to do the slow recovery, but I do need to take Fosamax). My non-operated hip is actually worse, so I very much want to rebuild bone density there longer-term if I can. I looked into Algaecal and it looks good to me, but the cost to take Dr Gross' recommended 2000mg/day is insane. A 60-pill bottle is $50 and it only lasts 7.5 days, so we're talking about $200/mo. I've been taking Nature's Way Alive calcium (
http://www.amazon.com/Natures-Way-Calcium-Formula-Tablets/dp/B007RMK3II/) instead and it seems very similar, but at a much more reasonable cost (~$40/mo to get 2000mg/day).
In addition to calcium, I'm taking magnesium and vitamin K2 based on other reading. I'm far from sure they help, but I don't think they hurt, and they're cheap.
Finally, and long-term perhaps very importantly, I'm going to make a big(ger) effort to do weightbearing exercise. I'd had to slow down with my hip earlier, but I want to get back to weightlifting slowly after I pass the 6-mo mark as a major way to stimulate bone density.
Hope this helps!