  We aim to determine the intrinsic variety, at a given mass, of the properties
of the intracluster medium in clusters of galaxies. This requires a cluster
sample selected independently of the intracluster medium content for which
reliable masses and subsequent X-ray data can be obtained. We present one such
sample, consisting of 34 galaxy clusters selected independently of their X-ray
properties in the nearby ($0.050<z<0.135$) Universe and mostly with $14<\log
M_{500}/M_\odot \lesssim 14.5$, where masses are dynamically estimated. We
collected the available X-ray observations from the archives and then observed
the remaining clusters with the low-background Swift X-ray telescope, which is
extremely useful for sampling a cluster population expected to have low surface
brightness. We found that clusters display a large range (up to a factor 50) in
X-ray luminosities within $r_{500}$ at a given mass, whether or not the central
emission ($r<0.15 r_{500}$) is excised, unveiling a wider cluster population
than seen in Sunayev-Zeldovich surveys or inferred from the population seen in
X-ray surveys. The measured dispersion is $0.5$ dex in $L_X$ at a given mass.
