A couple of my friend have been treated and had good results. It is expensive but it is labeled for lupus and insurance will cover it if your doctor advocates for it...medicare as well. Like all treatments, it is not for everyone and should only be considered if you have a severe and/or chronic case that doesn't respond to other meds.
As for expensive, think about IVIG which is what more myositis ( I have polymyositis) patients are using and it is off label for almost everything. Treatments range from $30,-50,000 per infusion! It was the treatment that saved my life 7 years ago but it is now 8-10X more expensive than it was in 2005.
Any of these newer biologics or IVIG are too expensive unless you are truly wealthy or your insurance will cover it.