...............I would put a value of once fired brass, especially 50yr old once fired brass, at well under what you would pay for new commercial cases. And this is assuming it is all once-fired, boxer primed, and in fairly good condition. It may have a value of of 10 to 15 cents a case, but someone really hard up for .30-06 cases may be willing to give more.
I've actually tried to pass on .30-'06 cases for now, even at a really great deal, as I've been able to obtain so much of it by keeping my eyes open for it at the range.(and a little digging around in range trash cans!) I even had a gentleman trade me out of about 200 once-fired 7mm Rem Mag cases, which I had in storage for about 8 years here in Texas. Some were a little tarnished/corroded to say the least, and I was upfront about it from the very beginning. I do not shoot 7 mag any longer, as I sold the rifle, and the cases were a holdover from before I ever started reloading. Needless to say he brought me well over 1000 .30-06 cases in 5 gallon buckets, somewhat segregated by headstamps, etc. Some was milsurp, some was commercial. I wasn't too picky as the 7mm mag stuff wasn't being used by me. Most of it the cases had the military primers(and crimps holding them in!), thus being once-fired.
He seemed tickled to death to get the 7mm mag stuff for the .30-'06 cases, even if they required a little exterior cleaning.
Once again, I am definately NOT the last word on price, as everyone's needs are different, and I feel that if you had asked this question 6mos to a year ago, the answer may have been a little higher from others looking for reloading components.