When do you use かかる and する when talking about how much something costs? It’s been giving me trouble.
As you know, かかる means “it takes”, while する means “to do”, so if you’re talking about how much something costs, you can use them this way:
この店に値段を下げさせるのに、暴力がかかる。
It requires violence to make this shop lower their prices.
店員が値段を下げないなら、暴力するよ。
If the shopkeeper doesn’t lower his prices, I’m going to use violence.
I think you can use する when referring to prices. (there’s a chance it could be slang, though, I’m not an expert)
For example: このオレンジは千円もするの?!
My understanding is that する refers to the actual price of something, its concrete value.
When you use かかる, it puts emphasis to the fact that it is your money that’s being used, and less on the value of the item.
I know. 
Sorry, I was actually joking. The likely origin of OP’s question is that Bunpro recently added the する (Cost) (JLPT N4) | Bunpro grammar point, which is difficult to distinguish from かかる (Time/Price) (JLPT N4) | Bunpro during reviews.
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I think someone else recently asked a question related to these new points. @JamesBunpro’s answer may help differentiate the two a bit more!
The new N5 points かかる and する - finding the difference impossible to grasp with the given examples
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