Like for a good one like Keurig, it cost like 300 dollars, while I also got one for less than 10 dollars.
What makes for the difference for the price difference in the coffee makers?
I'm going to isolate this response to only drip brewing machines since if we start talking about espresso, all my assumptions fly out the window.
Really you pay for the following on a machine:
Older drip brewers lacked a few things. The brewing chambers were simplistic, but the biggest downside was lack of accurate temperature control. Water needs to ideally be right at 205 F plus or minus a few degrees depending on coffee type, roast and age. Newer drip brewers rely on updated electronics that can accurately keep the water temperature in this narrow range which is going to give you improved coffee.
Look at the shower head at the top of the brew chamber. Does it pour the water down in a single stream, or does it distribute the water nicely across the grounds? This makes a difference in brew quality and on newer machines, more thought has gone into this design.
Pump rate -- if you read up on how people do pour over, a lot of focus is on timing. Allowing the coffee to bloom, then proper water per minute rates must be adhered to. All of these details will change the flavor of the coffee. Newer machines again have better control over these variables due to improved electronics which allow them to produce more consistent, and hopefully better coffee.
Thermal Carafe -- I just had to throw this in here; these machines brew into an insulated carafe rather than a non-insulated carafe with heater underneath. In my opinion, thermal carafes are amazing, and they have become much more available now that they once were. Nothing will kill your coffee faster than a carafe 'warmer' (I mean cooker...) under a non-insulated carafe.
You mentioned Keurig. Keurig is a whole different animal unfortunately. They have managed to corner the market on a particular brewing style (which by the way is inferior to old fashioned methods), albeit more convenient. You get the perks of the newer machines mentioned above in a $300 Keurig machine, but I don't believe the grounds chamber is big enough to actually brew a full cup of coffee, and I believe it brews too quickly to get a fully developed cup of coffee. Read thin and bright coffee compared to pour over, french press, quality drip. $200 bucks of the $300 goes either to the electronics of allowing you to brew a single cup at a time, validating it is a legit k-cup (they did away with the microchips in K-Cups I think?) or simply name brand.