I'll preface with this is just my opinion so don't shoot the messenger. You might first have to differentiate your pile into 2 categories, PS2 5V and PS2 3V. The wiring is similar but the connectors are just slightly different. Also some supporting equipment is different (example a 9V battery or BCR VS a 3V 2 cell or BCR) and a different speaker (16Ohm for 5V systems, 4 ohms for 3V). I guess you could get away with one common 16 Ohm speaker and both would play, but the battery/BCR , you kinda need the right voltage for a given board.
However, let's be honest here, if you have the older 5V boards, I would not test them. The price I might be willing to pay is vastly different between a 3V and a 5V. I'm not really interested in buying 5V boards if you say they work or not, testing them is literally zero guarantee they will work the next time they are powered. That's just the nature of that board series. I rate them just above scrap.
3V, you could test them, but since they are takeouts and I expect them to work (they are a pretty reliable board IMO), you testing them doesn't change my expectation on price. Especially since I don't know what you left for harnesses, these are not upgrade kits, so they are useful- don't get me wrong, and they definitely have value and a use case by people doing repairs and upgrades.
Further, are you then going to warrant the board given you tested it? I'm not saying that to be a jerk, I'm saying let's think this out. If you say tested and then it doesn't work, what's the remedy?
I had been buying cheap PS2 3V engines from a sponsor on the cheap typically under $140. However, that was complete and I had good complete wiring harness and a parted out engine when done. I also purchased a few PS2 3V tenders since the board and the bulk of the harness, speaker, and battery were all there, plus even an electrocoupler for $75-$80. Again, I still was getting trucks and frames and the usable parts so that plays into the math of what a bare board I was willing to pay.
You can ask whatever you want, I'm just giving one point of reference.