A lasting fallout from the Great Recession has been a sharp rise in the number of Americans who are renting rather than owning their homes. Sky-high real estate costs, financial insecurity and job instability have pushed many people out of the home-buying market and into rental units, especially in large cities. Following supply and demand, the increase in renters has come with an increase in rental prices. Those prices have eased a bit in the last several months, but there is a disturbing trend in the numbers : Rents for the most expensive places are declining while rents for cheaper places are rising, adversely affecting those on the lower end of the income scale. The Knowledge at Wharton radio show, which airs on Wharton Business Radio on SiriusXM , invited three experts to explain what’s happening in the rental market.…