It is hard to be sure, but we know some range figures for the missiles that have come before it.
The missile known in the west as Sunburn, or SS-N-22 which is carried on the Sovremmeny class destroyers and some light missile boats has a range of 120km and flies supersonically (1.8 or so at low level and mach 2.2 at medium altitudes) at a height of less than 7m. The highest altitude it attains is 300m to spot its target and then it drops down and attacks from below 7m.
Later versions were adapted so they flew at higher altitude for the first part of their flight and then dropped down low when they reached the radar horizon to the target, which extended its flight range to about 250km because jet engines are vastly more efficient in the thinner colder air at altitude, plus the fact that it is a rocket ramjet design the solid rocket fuel burns at a set rate for a fixed period of time... at very low altitude it would accelerate the missile to a max speed and then hold it at that speed until it burned out. By climbing however you more efficiently use the high thrust to climb to thinner colder air... the extra energy used in the climb can be recovered in the eventual descent, but the more efficient flight at altitude means moving faster for the same throttle setting which means a lower throttle setting can be used for the same speed or higher speed can be achieved.
Now the replacement for Granit and Sunburn (3M80) is Onyx, which has been revealed to have a 500km range at altitude and 250km range at low altitude and a speed in the mach 1.8 at low level and 2.5 at medium altitudes.
The Zircon uses a scramjet, which means the air intake does not need to slow the air flowing through the engine to subsonic speed for combustion.
To achieve mach 7-8 it will have to fly high but at that sort of speed it is relatively safe as long as it can manouver. The speed doesn't come at the cost of fuel... we are not talking about just dumping lots of fuel into an AB to get the extra speed, this is a much higher thrust engine that retains thrust at very high speed, so flight range should be vastly increased as well as speed.
I would expect a flight range from at least 500km to maybe 700km but only at high altitude.