This might be an extreme example. I just had dinner with a med onc who told me the rates are more commonly like 2-4K a day in rural places, but this includes call, inpatient, and longer hours of infusion center coverage. This is still higher than RadOnc, but Im doing locums right now for 2000 a day... but an 8 hour day, not a 24 hour day. And it's an easy day. So to me that "scales" to almost 10,000 for 24 hours (that I would not do).
If a place is struggling to find coverage and they are offering you 1900, ask for 2400. I never even thought to negotiate, but it was recommended to me by the company middle man! You can feel very good negotiating especially if this is a job you can do on a recurring basis and they like you. I will be doing that next time.
Im no economist, but these seem like basic market forces on a local scale. If the local Rad Onc is pissed s/he can't take a vacation, the hospital is struggling to find coverage, and you're the only one that will offer it... sounds like you are in a pretty strong position to ask for a (IMO) more reasonable rate than 1900.
I'm on board with complaining about the overall market, but certainly you can get a much better deal locally in many circumstances.
Note: just thoughts based on my very narrow experience doing some repeat locums for a single clinic.