What airspeed is required at sea level to create the same aerodynamic pressure as cruise altitude?
You are looking for the equivalent airspeed. Here is the definition from Wikipedia:

Equivalent airspeed (EAS) is calibrated airspeed (CAS) corrected for the compressibility of air at a non-trivial Mach number. It is also the airspeed at sea level in the International Standard Atmosphere at which the dynamic pressure is the same as the dynamic pressure at the true airspeed (TAS) and altitude at which the aircraft is flying.

$$ \text{EAS} = \text{TAS} \times \sqrt{\frac{\text{density at altitude}}{\text{density at standard sea level}}} $$

At standard sea level, EAS is the same as calibrated airspeed (CAS) and true airspeed (TAS). At any other altitude, EAS may be obtained from CAS by correcting for compressibility error.