It is never simple cost per kg calculation . Ridshare orbit depends on the primary orbit requirements, if the orbit is not favourable to your sat, correcting

It is never simple cost per kg calculation . Ridshare orbit depends on the primary orbit requirements, if the orbit is not favourable to your sat, correcting the orbit may not be feasible at all, given the small payload size you may not have the fuel for the correction burn Also fitting your sat to a rideshare payload adapter could be lot more complex depending on the primary and other shares Similarly while spaceX is cheap, there are plenty of workloads where ULA is the only option, vertical assembly , certain fairing sized , some orbits etc .