Evolution is a long, painful process for most halflings. It takes anywhere from a week to two weeks. Along with the pain of growing new ears, horns, or tails, or having existing details fall off, things can commonly go wrong with the evolution process. New growths can get infected, bones might not set properly, etc. Special doctors may be hired to ease the pain and growing process, but this is usually very expensive. It is more common to see nobles and their children evolved and less likely to see peasants in higher evolution forms.

The halflings that make adept evolution therapists are fighting-types (good for physical therapy, knowledge of muscles and bones), psychic-types (mental focus, easing pain, etc), and some normal-types (they know a lot of healing moves). Usually these professionals are roaming healers, but in some of the larger towns, one to three may be found residing at the temples.
Everstones are more readily available, and cheaper, and many halflings end up carrying them instead of risking a botched, painful evolution.

There are numerous drugs and concoctions (many illegal) that some halflings take to lessen the pain. Problem is - these are very addictive, and don't guarantee a proper evolution. They just offer a trance-to-coma-like state for the person. In the case that they make it through the process without any infections or abnormal growths... they usually have developed a dependence on the drug, and continue life as an addict.