From each room thermostat, a cable must be laid to the respective heating circuit distributor (I assume you have two). Additionally, each heating circuit distributor requires a supply line, and last but not least, the room thermostats must also be connected to the actuators on the HKV. This is quite an effort and results in a considerable length of cable. I can say this from experience because I did this myself a few weeks ago in my new building (172 sqm). 750 € is not a bargain, but it is certainly not too much. The 59 € is - as mentioned several times - only the material price for the room thermostat.