Lithium goes by level, not dose, but you're on quite a bit so it may not increase much. Valium isn't used that much and honestly 5 mg knocks me out for many hours so I don't know about it; I'm surprised they are using it as klonopin and ativan are more commonly used. Seroquel can go up a lot from 200 (800 is the max approved dose; I've been on 1500 mg before). I don't know the dosing for Zoloft.

There are ways to get meds cheaply. Most name brand meds have patient assistance programs that give you meds for nothing. I use them for a few meds I couldn't afford otherwise. There are also programs like rxoutreach.com that drastically reduce prices and goodrx.com that help you find the best prices. But there are lots of generic meds that are quite cheap out there. You just have to tell the dr that cost is an issue. Again, social workers can help here. I would think you should be eligible for Medicaid. (Which in my state provides transportation to visits as well as covering drs, hospitals and meds)