Methadone is what I think you are referring to. Very inexpensive still --(unless the FDA does something to change that! )

It has to be used with care, because it is the only opiate that affects conduction of the electrical circuit in the heart. At high doses this can become problematic, also additive with certain other drugs that do the same thing, or may affect normal people who become dehydrated or low in the electrolytes potassium and magnesium.

Some doctors don't screen people properly for this, so it is up to the patient. So everyone starting this pain reliever should get cardiac screening for QT potential.

More here;
http://www.azcert.org/

The other drug mentioned here is Suboxone, and it is quite expensive and only certain licensed doctors can prescribe it in US at this time. It is used for tapering people off heroin or RX opiates but also is finding a niche as a pain controlling agent as well and there is some evidence for drug refractory patients with depression.