They already expect you negotiating the offer that's why they lowballed on your expectations. 40 to 30 is already 1/4th of a cut in negotiations.

Just call them up and say all the nice things like great company, thanks for taking time, but then start counting your strengths and finally say that I think I bring a lot more value and these were my expectations and please think and talk about this internally and let me know.

They will most probably come back with a higher number.