Books are becoming middle class economically aware

Update:
As some of you pointed out: excessive usage of budget might indicate Nation's budgets instead of personal budgets.

At least that is what the usage of terms cheap, expensive and budget in books over time tells us (via Google Ngram):

Usage of the words in books (click here to see the webpage)

This graph shows out of all (uni-grammatic) words used in books published each year, how many of them were cheap, expensive and budget. More details on interpreting the graph are here.