We construct a generic unified model of sources to account observations of ultra-high energy cosmic rays at $\gtrsim 10^{19}$~eV as well as high energy neutrinos above 100 TeV in a framework of photomeson interactions. The mildly efficient in-situ production of $\gtrsim 100~{\rm TeV}$ neutrinos with $0.1\lesssim \tau_{\gamma p}\lesssim 0.4$ must be realized in a source environment to accelerate cosmic rays to ultra-high energies. The measured fluxes of cosmic rays and neutrinos set the bound on the source luminosity and the emission rate. Tidal disruption events (TDEs) and low-luminosity GRBs are consistent with the present requirements if the Lorentz bulk factor of plasma and the equipartition parameters for cosmic rays and magnetic field are appropriately selected.