The cost of treatment depends on several factors, the most important of which is where you live. This forum is based in the UK and most (but not all) of its members live here. In the UK, if you're normally resident (and I'm not sure how that is determined) then practically all medical costs are covered by the NHS - essentially, it is an insurance scheme that covers all costs for everyone who lives here. That means that the cost of treatment for cancer or just about any other disease is free.
I believe much of the rest of Europe has similar schemes, but each has their own rules for who is eligible. Outside of Europe, many other countries also have their equivalents.
The main exceptions I can think of are India and the US. Both these countries have private medicine, but the costs differ wildly. In the US, unless you have insurance or are covered by the very limited US Medicare scheme, cancer treatments can cost hundreds of thousands of dollars. My understanding, although I haven't studied this in detail, is that private medicine in India is far more affordable.
Canada has a free health service similar to the UK. I don't know the situation in South America or Africa.
As you can see, this means that depending on where you live, the cost can vary from essentially nothing to a hundreds thousand US dollars. Without knowing where you live, it's impossible to be more accurate.
