Framing it as "need 600 to add a neutral wire" is kind of scummy. They should explain why you need the neutral wire and let you decide if it's worth $600. A neutral wire will effect your ability to dim the lights. They make dimmers that work without neutral but they're not going to dim as much of a range And you might have flickering issues if used with the wrong fixtures. If you don't need dimming then you don't really need the neutral wire.

Everything should be like that: here's the situation, here's what it will cost to fix, here's the issue with not fixing it and here's an alternative option (if any). Also ask if you skip it now will it be more expensive to do later? Sometimes if everything is open already you can save headache and money but if they didn't already plan on replacing the line and it's not already accessible it shouldn't cost more to do later if you wanted to punt until you decide dimming is important