I'm certainly no mathematician, but... if we stay with the $2.6 Billion number and divide that among the 307,006,550 people living in the united states (according to the Census Bureau) then the cost of the census averages out to about $8.50 / person counted. If the benefit to communities from having residents counted is about $2,000.00 / person then is seems to me like it's a pretty good return on the investment.
While the total cost of the census is probably higher this time around, I don't think it will get so much higher than the $8.50 / person as to make the $2000 return not worth the effort. Also, consider that if we cut the cost of the census, then we wouldn't know where to allocate the money that was saved, or at least it would very likely no be properly allocated.