We power the SUP, DUG, DUL, RUS units with some industrial PSU 48v from for example the brand "MEANWELL". 600 Watt version is not excessively expensive. We did get a couple of PSU 01 (I think that is BML 161 174/1) partly because I was interested in seeing if I could just connect to the EC system and then monitor such as input voltages and current draw with the DUG. One of them died very shortly after an ex-colleague shorted the output while trying to jury-rig the very proprietary connector. So one might assume they are not abuse proof, fair enough. Of course, with all this decommissioned gear, you never know quite what you get or what it's history is. Also, it's designed to go into an enclosure, you'll need to cool it somehow, not a difficult task, but requires effort. All in all, I wouldn't bother with them, Adding a fan to something like the meanwell is not hard, but actually I haven't had problems with them with only ambient cooling.
We do now have a fancy solar system, designed at a national university, with isolated configurable multivoltage outputs so we can run both - and + ground systems off the same battery bank, with both panel and AC (grid) input. I'm pretty sure the design specs of that thing are open. Not sure where they may have been published though.
We've stopped trying to acquire more Digital and Radio units for the time being, but as far as I am aware, (I wasn't directly in charge or involved really in acquisitions), the surplus suppliers did have quite some availability of DUG/DUL units. What we found hard to source was Band 5 RUS. I did recently glance at ebay looking for a DUS; There can be issues with the firmware on these units, and I was wondering if the DUS might have something more recent available. I didn't get anything, but I did see some DUS available and they were not "relatively" expensive.
Now, IF one were to really desire to run a production 2G cell using Erissson surplus gear, I'd concur with Harald, use the DUG/RUS.
You're going to find hiccups already with that and some bugs that still need to be ironed out to make it production ready. I haven't had a lot of success with the GPRS/EDGE on it, - it has been observed to "work" under laboratory conditions with certain UEs, although I imagine that it is probably very close to a possible production network, it may just need more people to actually test and fix with a variety of phones and configurations.
If the desire to not to run a production network, but to fix and create further implementations of whatever in FOSS, then I guess it's up to whoever wants to do it to decide if they want to put effort into SIU or whatever.
Anyway, a quick glance at ebay (not to promote that site) will show that there is a bunch of DUS/DUG/RUS etc gear available, not far off the 300 yoyos that were mentioned in 2018 for a DU/RU combo, albeit sold "as is" so you may run the risk of getting some dead gear.