If you ever visit Pittsburgh, there's a place in Squirrel Hill called Jerry's Records. They have a floor inventory of over half a million records (they claim 1 million), most priced at $3-$5. The major label USA pressings of Beatles stuff is cheap there. They also have fairly priced Beatles UK issues (typically $65-$125). You could easily spend 8 hours rifling through the inventory. Bring allergy pills... the place will set off an allergy attack for anybody with mold / mildew allergies.
Jerry's Records :: The World's Finest Vinyl :: Pittsburgh, Pennsylvania
I've been picking up rare issues of KK Records Belgium & 3rd Mind Records (Vancouver) releases at his store for years.
Avoid flea-markets... most people there let the records sit vertically in the sun, making a speed bump / bicycle jump out of the vinyl.