What is the mass and momentum of a relativistic jet?
I am not expert in that field, but I found a number and a reference:

A paper by E. Memola et al. on Theoretical thermal X-ray spectra of relativistic MHD jets assumes a mass flow of $\dot{M}_{\rm jet}=10^{-8}M_\odot {\rm yr}^{−1}$ for a central object of $5 M_\odot$
The paper The theory and simulation of relativistic jet formation: towards a unified model for micro- and macroquasars by David L. Maier (see also arXiv/astro-ph/0312048) looks like it may contain more insights, but I did not go through it in detail.