two Y Axes (in the same scale) in ggplot2

Dear R users,

I'm plotting housing prices in City A over past 30 years in ggplot2. The Xs
are years since 1980. I have two housing price variables: new home prices
and old home prices, both of them measured by $/sqft. I have searched
related threads on multiple Y axes in ggplot2 and I understand that multiple
Y axes in different scales are not possible. I'm wondering if it is possible
to have multiple Y axes with the same scale in ggplot2, like in my case. If
still not possible, is there a easy way to do it in R's default plot
function? Thanks.