Don,
If the PRO charges more than $7.50, including postage (which I think they will), you ought to look into the MilSpecManuals version. Their website is at
http://www.milspecmanuals.com/ On that page put in Ploesti in the search box, tick the Title line, and search. It will come up with 5 items. One of which I think is your book. They will be quicker for you than for me, because they are just across the border in New Mexico.
Just as a note for anyone else, the site has prepared PDFs of many "manuals". The US Strategic Bombing Surveys are there. The three volumes of Red Baron 1 from Vietnam are there. Worth exploring, but it can take a while!
Enjoy!
Frank.