Warning. Gross generalizations based on quick price checks and careless price tracking ahead. 😉 I'd recommend doing your own price research by looking at completed sales either in your area, eBay, etc.
It all depends on the condition of the camera and lens. A perfect, scratch free, like new Summar seems to go for around $300-500. Cosmetic issues but very good glass drops it to about $300. Some cleaning marks drops it down to around $150. Por condition evidently drops it to $40 based on a recent thread.
Similarly a IIIc seems to vary in price between $75 for a non funtion camera in need of work to $300 for a good condition, recently CLA'd camera. It looks like users tend to go for around $200.
This is where it's really hard to assess without hands on use of the camera. Even then, it's difficult to know the state of the curtains until you shoot a roll. I was fortunate enough to buy a III with a Summar here for $325. The camera and lens has been DAG CLA'd within the last decade and the glass was in excellent condition. My gut feeling is that there are better deals for users out there - the price is bordering on mint/collector prices - but you know more about what you are looking for, how much info you get about the condition of the camera, how risk tolerant you are, etc