It's a Monoclonal antibody - those are some of the most expensive drugs there are (i.e. hard to make in bulk). Add to that how difficult it is to administer (keep frozen, thaw slowly).
We (appear to) have a way to stop the epidemic, yet we can't actually do it.
There is a lot more to stopping an epidemic than creating the drug. You also need to be able to administer the drug--and in some of the areas worst-hit by the current outbreak, residents are suspicious (or actively hostile) to medical teams.
Ebola transmits through direct contact with bodily fluids, which means that basic measures of sanitation and hygiene can go a long way toward slowing its spread. If those cannot be achieved, distributing an expensive, delicate drug is not likely to be achievable either.
Antibody drugs are being made in bulk without too much difficulty. There are a number of RA-specific drugs on the market that are doing well, and at least one of them is grown in 6000-litre fermenters. Yeah, there might be problems getting this set up and approved, but the technology's been in place for a decade or two.
To be fair, the ultra wealthy were already safe. It's pretty easy to avoid sick people (particularly sick people spewing blood) when you can just hang out on your island or on a large estate.
Or any room that lacks someone currently dying of Ebola or recently dead from Ebola. I'm pretty sure the only victims are caregivers and people who deal with the dead - it's not easy to catch.
We (appear to) have a way to stop the epidemic, yet we can't actually do it.