I just picked up a used late 2008 Aluminum MacBook5,1 2.0 GHz 13", for less than US$150 used. I put in an SSD and 4 GB RAM (which I already had, so they didn't cost extra), and then used the installer patcher to install High Sierra.
Initially it had 2 GB RAM and 160 GB hard drive with 10.10.4 Yosemite on it, and it was totally unusable. I don't know how the previous owner was able to tolerate it. It would take forever to do anything at all. However, with 4 GB RAM and SSD it's definitely usable. Surfing is somewhat slow, and even the 2009 2.26 GHz MBP5,5 I have is noticeably faster, because at these speed levels, every little bit (13%) counts it seems. I'm thinking for a 2009 machine an ideal CPU would be 2.5-3 GHz.
Too bad it was so slow because it hid a minor defect in the trackpad in this used machine. In one spot you have to press a bit harder to make the click work every time. If you press lightly in that spot then it doesn't always register. Fortunately, the rest of the trackpad is fine. I didn't notice it before when I was testing it because I had to fight the spinning hard drive and 2 GB RAM to do anything, so missed clicks were not a surprise, as I'd often have beachballs. But now that the system is much more responsive with 4 GB RAM and SSD, any small problems like that can be noticed. Let that be a word of warning to you if you're scouting the used market for old machines like this.
But overall, I'm pleased. I now have another operational and reasonably responsive High Sierra machine for under US$150. The 2008 white MacBook4,1 we had before was problematic, because we couldn't install any modern browser on it, so it had to finally be retired. BTW, I put the HD in it and yes, it's back to being painful to use performance wise. Even though it's retired, if I find an uber cheap 60-120 GB SSD somewhere, I'll buy it for this machine.
Also, I will reiterate that if you plan on buying one of these old machines for your primary driver, don't skimp out on RAM. Even with my light usage, it was easy to hit the swap with 4 GB RAM.
I had over 1 GB compressed RAM and a larger swap. This screen grab from Activity Monitor was a while later.
My MBP5,5 with 8 GB RAM is obviously much better, and I could use that as a primary driver in a pinch, although obviously my 16 GB MacBook Core m3 is in a totally different league.