I was looking at some 1905 divorce records the other day and noticed that my great-grandfather owed $2.50 per week in child support. Since he worked as a day laborer, timekeeper, and as a machinist, I suspect that the $2.50 represented a significant amount for him. To find a more precise answer to questions like this, I used to use NASA's inflation calculator, but recently I found a set of calculators that I think are very impressive.
The site is called www.measuringworth.com.
One of the things I like best about it is that it uses data sets for currencies from the UK, US, Japan, and China.
It also provides several calculators: