See this conversation:
B: This t.v is $2500.
A: You can't be serious.
B: That's how much this t.v costs.
A: That's too expensive for me.
B: This television is of very high quality.
A: You can't go down on the price.
The structure "to go down on something" does not exist in any dictionaries. However,
we have "go down (on somebody)": (slang) to perform oral sex on somebody (= to use the mouth to give somebody sexual pleasure)
I reckon this is some sort of creative use of the "to go down on somebody", so "to go down on the price" means "to ease the price" just like when you go down on someone you ease, please & give pleasure to that person.
What does "go down on the price" mean?