[TYPES] Why are ACM conference registrations so expensive now?

[ The Types Forum, http://lists.seas.upenn.edu/mailman/listinfo/types-list ]

Hi,

I just registered for POPL, and the total cost was over 2000 USD. This 
seems really high, and it seems something that has gotten a lot worse 
over the last year or two. For example, ICFP a few months ago was 1500 
USD, and POPL last year was 1375 USD.

Does anyone know what factors have been driving up the cost of our 
conferences up so quickly? I'm worried we're making our events 
inaccessible to anyone but the best-funded researchers and institutions.

Best,
Neel