Others are still finding places to buy, even if today's cheap stock is very different than the cheap stock of five years ago.
"Undoubtedly, it's much harder to find good value today," said Charlie DyReyes, senior research analyst for large cap equity strategies at Brandywine Global.
DyReyes says that his team constantly runs programs to screen to hunt for attractively valued stocks, and these screens are now producing "a much shorter list than we saw three or four years ago. And the companies that are on this list definitely have a lot more hair on them."
While the stocks that used to be cheap "were cheap for no reason, now we have to wonder why they're cheap," he added. "We have to be careful that we're not buying broken companies."
Still, DyReyes says that he still spots "pockets of value," including in large-cap banks such as JPMorgan and Wells Fargo, private equity companies such as BlackStone and KKR, and energy stocks like Continental Resources.
"We're finding value in select energy companies, which we bought starting in December and through to today," he said. As oil prices plunged, "the baby is getting thrown out with the bathwater. We see this as a once-in-a-multiyear-period to buy energy companies much cheaper."
Similarly, David O'Malley of Penn Mutual Asset Management says that energy and metals and mining stocks are two of the rare sectors in which bargains can still be found.
"The deep value is in places where there's so much bad news priced in that even if there is bad news, they won't fall further," O'Malley said. "If you look at stocks like BHP Billiton and Rio Tinto, these are global enterprises and great companies, and they're trading at great values and paying attractive dividends."
On the whole, however, the value-conscious O'Malley predicts that "this is going to be a difficult year for stocks."