When you or your friend arrive at Santiago, head over to the Pilgrim House, #19 Rua Nova. They usually have a quite a supply of assorted trekking poles, abandoned by their previous owners. They are closed on Sunday and Wednesday, but open other days from 11:00 to 20:00.
When I was working at the pilgrim office this past July - August, they actually asked me to stop bringing more trekking poles as their donativo box was full. Instead, I reverted to only bringing them the best quality poles, that were still functional.
At the Pilgrim Office, there is a green and yellow box in one corner of the courtyard where pilgrims are requested to deposit their no longer needed or wanted wooden walking staffs. This keeps the courtyard neater.
Eventually, a local charity retrieves these wooden poles to be cut down for wood stove kindling. Yes, there are still some old homes in and around Santiago that still use wood for cooking or heating.
But, you would not believe the higher quality poles that people abandon here. One of my daily duties was to triage this stash, removing the steel, aluminum, and carbon fiber hiking poles, as well as the metal tipped wooden staffs many pilgrims buy along the way.
The metal tipped, store-bought wooden poles were placed to one side as many pilgrims seek these are continuing on to Finisterre or elsewhere. Instead of having them rummage through the sometimes large pile, I separated the best wooden staffs out. I have no idea what they do about this when I am not there.
The modern poles are evaluated by me. The "crap quality" poles go directly into recycling, adjacent to the trash. This includes most of the souvenir shop "anti-shock" heavy, noisy poles. The functional, best-quality poles are carried over to the Pilgrim House by me, so they can be placed into donativo exchange and returned to service.
The least good among this group would be anything sold by Decathlon. Burt, Decathlon sell poles are varying price points. Some are better than others. But, I tested all to ensure they adjusted properly before repurposing them.
I scavenged Leki, Elementerre, and Black Diamond poles daily, at least while I was there. Frankly, I was surprised by the quality of some of what people just placed in the bin, or leaned against the large trash container in the courtyard.
On my regular trips across the courtyard and in the front of the building, I regularly picked up evidently abandoned poles for recycling, one way or another. However, hiking poles found inside the building proper, like in front of the processing counter, were usually kept for a few days to see if someone came back looking for them. Pilgrims rarely did. But, we did wait before recycling those poles.
So, if you find a decent pair of poles at Pilgrim House, test them to make sure they adjust properly. I believe that they will tell you you are welcome to the trekking poles.
HOWEVER, please do remember that the Pilgrim House operates on a donativo basis. Ask about this, and do be generous. Tell them I sent you...
I hope this helps.