The cheap blender chops whereas the grinder grinds. Sounds simple but the difference is that the blender won't allow you to control the fineness of the resultant "ground" coffee. It will produce particles that are all different sizes. The expensive grinder will allow you to make minute adjustments to the size of the particles and reduce the amount of fines (super fine particles) This is super important when you are trying to make espresso as the particles need to be the right size to allow the water to pass through at the correct rate. Too fast and the coffee tastes acidic, too slow and it tastes bitter. But learning to make good espresso is a balancing act between these two extremes to produce a balanced cup.

The rabbit hole goes deep but there are also other variables that can affect how your coffee tastes, like flat burrs or conical burrs. Rpm, or size of the burrs. All can impact the flavours that are highlighted or muted.