Frost Lotus is a component of raiding flasks, and it is gathered as a very rare chance from regular herb nodes, as well as Frost Lotus nodes that appear in Wintergrasp and Freya's room in Ulduar. The price of Frost Lotus has skyrocketed since patch 3.3 on many servers. This is partly due to the large increase in demand for flasks that the new content brought us, but I believe partly because of a reduction in supply.
The supply of Frost Lotus is and always has been low, however as I mentioned in my last column, there are ways to farm it. The most popular one was to get saved to an Ulduar raid ID where Freya's Elders (Brightleaf, Ironbranch, and Stonebark) have been killed, but Freya herself hasn't, allowing the herb nodes to respawn. Getting the nodes to respawn simply requires a "soft reset" of the instance, which means nobody zones in for 30 minutes.