a (good/great) deal
"Getting a good deal on something" means buying something for a really low price. For example, if you're looking to buy a new car, you can say:
I haven't bought one yet because I want to wait around and get a really good deal on it.
You don't always have to use "get" and "on (something). You can just talk about "a good deal":
Five for ten dollars? That's a great deal!