I don't see how something like high dose vitamin C IV is very expensive. I would assume a handful of oncologists could do the whole thing themselves. We get X patients a year, we randomly suggest the vitamin C IV to half, the half with vitamin C did better or worse by these metrics. Vitamin C is not expensive and they have to collect the outcome data for everyone involved anyway - so where is the expense coming from?

If it has benefits then more doctors will start to do it and more data will become available. If not, onto the next thing.