Washington is 34% more expensive than Richardson.
When comparing Washington, DC and Richardson, TX, the overall cost of living indices are 171 and 128 respectively (national median = 100). Rent is $75/month cheaper in Richardson, saving renters about $900/year.
Median household income is $10,030/year higher in Washington. Home values also differ significantly — the median in Washington is $724,600 compared to $405,600 in Richardson.
Texas has no state income tax, giving Richardson residents a significant tax advantage over District of Columbia's 10.75% rate.
Washington vs Richardson — common questions
Other cost of living comparisons for Washington and Richardson