History of the phrase <<Everyday Low Prices>>

[RonButters at AOL.COM]

A colleague here in North Carolina writes:

<<I'm writing about Wal-Mart, the
retailing giant, and I'm trying to track down the roots of the phrase,
"everyday low prices." It's one of their long-standing slogans.>>

He has checked the obvious sources, including Nexis back to the beginning.
Anyone done anyh research on this particular item?