Monitors are one the most important pieces in a studio. Each monitor shape the sound in a different maner. Some are said "flat", meaning its output faithul result, others are said flattering, meaning its emphasized some frequency to sound more appealing to the engineer.
Monitors are always sold per speaker. Meaning, that if you want to have a stereo set (which is what everyone do), you need to multiply the price two times to get the set price.
Most of the monitors are active. This mean that the amplifier is in the monitor and that you don't need to have an external amplifier (which is needed if the monitors are passive).
Each speaker also have a frequency reponse range where its perform or not. To have the most equilibrated sound, in terms of frequencies, it's often a good thing to buy a sub-woofer in complement of the two speakers. The bundle of 2 speakers and 1 sub-woofer is called a "2.1 system".
References :
- [Neumann KH80 DSP](https://www.thomann.de/fr/neumann_kh_80_dsp.htm) - ~460€. Knowed for a high fidelity sound with a wide frenquency range. This model have its own DSP to for dynamic frequency cut (the frequence limit under wich the speaker delegate the sound to the sub-woofer). Should be combined with an external sub-woofer. The [Neumann KH 750 DSP](https://www.thomann.de/fr/neumann_kh_750_dsp.htm) is the natural choice.