Negotiation language leaves room. A blunt 不行 (no) sounds harsh; softer phrasing like 这个价格有点难办 (that price is difficult) or 我们需要再商量一下 (we need to discuss) is preferred.
Quoting
我们的报价是…… (Our quote is…); 您这边能接受的价格是多少？ (What price works for you?); 能不能给个更优惠的价格？ (Could you offer a better price?)
Bargaining & Concessions
如果量大，我们可以适当让一点 (For larger volume we can give a little); 这是我们的底价了 (That's our bottom line); 各让一步，怎么样？ (Shall we meet halfway?)
Closing
如果没问题，我们今天就可以把合同定下来 (If all is well, we can sign the contract today); 希望我们合作愉快 (Hope we have a great partnership).
Cultural Note
Chinese negotiation values 关系 (relationship) and long-term trust; the pace may be slower. Patience beats pressure.