Not sure, but diplomats currently cost 700 hammers in Modern.
In terms of happiness, in my current game (playing Egypt as a Tradition/Artistry CV play). Until Industrial I pretty much stayed between -8 and -2 the vast majority of the game. This was without any serious focus on happiness management, just the occasional corrective measure. By Industrial I was able to get the Industry Finisher that gave me a tremendous boost to happy. Now in Modern, I'm at +38 happiness. I will say, that at -10% needs for all of the needs buildings, I wonder if they actually make any real difference in your happiness now, compared to the -30/-40/-50% you used to see.