I usually check to see if the library has the ebook. If not, I will check to see if they have the pbook.
This price differential has just about eliminated my impulse book buying. I used to go on book buying sprees several times a year, buying hundreds of dollars of pbooks at a time.
Now, if I want a particular book, I look at the price on Amazon. If it is a back list book, and it is less than $8, I will buy it, even though I could get the pbook for less. I don't buy new releases at all (if it is something I have to read, I reserve the pbook at the library). Once agency is gone, I will buy new releases again.