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?
Best Answer
The other definition of "to go down on somebody" you found is totally unrelated.
Basically, when prices go down, things are becoming cheaper. The numbers start out big (e.g, $50) and they end up small (e.g. $10), so they are going down.
For example, someone might say "That game costs $100, but I only have $50. I guess I will have to wait until the price goes down before I can buy it."
In your case, person A is asking whether the TV can be sold for any less money. "On the price" means "concerning the price", as in "We need more discussion on the matter."
Person B might respond "Sorry, that's as low as it can go", without giving any discount, or he might respond "Tell you what, I'll sell it to you for only $2000".