Well, a LimeSDR based E-UTRA (LTE) Band 38 2x2 eNodeB could be had for a couple hundred USD, depending on how cheap you can get the Host computer and clock sour

Well, a LimeSDR based E-UTRA (LTE) Band 38 2x2 eNodeB could be had for a couple hundred USD, depending on how cheap you can get the Host computer and clock source. I'd consider just injecting the clock via the fiber (running a dedicated single-mode fiber from the next PoP (up to ~10 km away) to the eNodeB, potentially exposing Ethernet service from the base station, just like the typical monolithic DOCSIS wifi router), via one of two ways: (1) run a separate wavelength via CWDM and just AM-modulate a sinusoidal reference oscillator output onto it, or (2) anchor the clock for the data link from the PoP to the eNodeB to your reference oscillator, and just tap your reference clock (to feed into the local VCXO-based master-PLL) off of the data link receiver's clock recovery circuity. Some mild phase noise is acceptable thanks to the VCXO.