Finding CB large monitors is always a challenge. Black throats are nearly always WC, waters too. Although NERD and Prehistoric Pets both breed waters but NERD breeds albinos, so the cheapest ones are over 1000 (for 66% het, the albinos are 15,000 !), and PP breed for the sulfur trait, so they're 1500 (100% hets, 2500 for sulfurs). Neither of them produce normal monitors, they only produce albinos, sulfurs, and hets of the either of them. If your dead set on a CB (which is always a good thing) go for Argus Monitors. Nice patterns, fairly large, active, readily available, and interesting behavior.
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Jason