What differentiates a $100 coffee machine from a $1000 coffee machine? There is a huge amount of price variance for coffee machines. Just a quick look in any shop will reveal two espresso machines, made by the same manufacturer, one in the $100 range, and another in the $1000 range. For the purposes of simply making espresso from ground coffee, what is the difference between them?
More expensive coffee machines typically have better "plumbing", including some and even all of the following:


2 boilers / HX to allow for frothing and brewing at the same time
Preinfusion
Copper boilers vs. cheaper aluminium versions (guarantees better temperature stability)
Larger boilers, allowing for more shots to be drawn/ milk to be frothed
Wider portafilters (which in some peoples' opinion gives better flavour)
3-way valves to allow back-built pressure to evacuate
a real steam wand, no gimmicky plastic ones that promise the world and don't deliver
the ability to be plumbed (connected to your water drain so you don't have to manually clear out the water tray.)
The option of vibration vs. rotary pumps (which are quieter, although I think they are more likely to break if there is no water)
Customisability of technical factors (pressure, temperature) which gives more control for our crazy data-obsessed coffee needs :)


Now this doesn't mean you can't get good coffee on a cheaper machine. You're just going to have to put more effort in it and get more variable results. Which is more than fair for most people.

As for the price difference, most of these features will raise the price by themselves and a lot of the more expensive machines are hand-made as well.

Last point they are also very pretty and a status symbol, not to the extent of let's say a very expensive watch but it does sort of feel that way sometimes.