I would recommend removing a female to a separate tank when you notice she's "holding" eggs in her mouth. That way, she can carry the eggs to full term without being harassed by the males and other fish.
After the babies are released, it's a good idea to leave the female in the nursery tank for at least two weeks before reintroducing her to the main tank. You have to remember, she's eaten very little- and possibly NOTHING- for two or three weeks. She'll be hungry and weak- which is no condition to be in with anxious males around. Leaving her with the fry will allow her to build her strength back up and withstand the rigors of mating/breeding.
Do you know if your mbuna are Metriaclima zebra (the common zebra), or perhaps Metriaclima mbenjii (Red Top Cobalt Zebra)? The mbenjii are usually more expensive than common zebras. Price will really be determined by your local market. I've seen them sell from anywhere between two and ten dollars in my area.