My absolute favorite flats are from the Gap; I currently own two different styles of their basic black leather flats and I wear them constantly (when the weather permits). I love them because they look luxe and are made from soft, genuine leather, yet cost so little! Despite the fact that they have almost no cushioning and very little arch support, I can wear them for hours without pain.
Here's your basic black flat, just $39.50:
Here's your basic silver flat (also $39.50), wear it like any neutral for day or night:
Gap has dozens of options, love those cap toe flats:
If you're certain you need a more supportive sole, check your nearest Marshalls Shoe Megashop for genuine leather flats by Me Too (as seen here) - super cute style, cushy footbeds for under $40!
Who makes your favorite flats under $40?