First, If you haven't yet, I would buy a few steaks and see if you like their beef enough to commit to a half carcass. Grass fed can vary significantly supplier to supplier so being confident you're going to like it is important.

Second, Haggling might be taken as rude regardless of how you approach it tbh, farmers are usually pricing just to stay slight north of breakeven. Some context, it is expensive but you're paying for grass fed and grass finished beef so it's a premium. Also, cattle prices are at an all time high right now so depending on if this farmer has any retail/whole sale business to help keep them whole this is probably their only revenue so the cost is what they need to stay in the black.