Well, I'm a couple weeks late to this party, but here is my MAC portable story. About a year ago, I was able to buy a non-working 5120. Complete with original carrying case, manuals basically everything for $125 from a local owner/collector. He was moving and wanted to clear some stuff out. ( I got several more thing from him as well for free) He said it used to work when he got it but was obviously dead now. I spent approximately another $250 on recapping, new batteries and an RAM upgrade card from Androda, etc. I DID NOT replace the hybrid module. (I was clueless on those issues) I was able to recap it myself, including the screen and trackball. It was fairly easy to work on. Once I had it all cleaned up, It booted right up with the original SCSI hard drive. Yes, you read that correctly. The original SCSI still worked with no issues, no stuck heads, no work to it at all. The screen was perfect except for one small thin vertical line on the right side. It also had a defective mostly populated AE MacRAM portable card in it that kept it from booting when installed. I listed the AE Mac RAM card on ebay with the bidding starting at $20 with a buy it now of $100. It sold almost instantly for $100 buy it now. I guess I should have asked for more, but as I mentioned earlier, I was clueless. I wasn't sure if there was even any interest in a non working portable RAM card. Oops. After about a month or so , I was tired of playing with this beast of a machine so I decided to list on ebay and move it along to someone who really wanted one. I don't remember exactly what it sold for but it was over $1300. The highest price I've ever gotten for any piece of vintage tech I have ever sold. I was also able to sell a few other related things that came with the portable (extra power brick, ext modem, etc). All in, I cleared over $1000 in profit on that thing and I was just having fun with it, learning a lot along the way.
Yes, I believe I got lucky in more ways than one starting with the price I paid and no hybrid issues.
Since the OP wanted advice on selling one.....
Knowing what I know now, If I stumbled across another one, I might take a chance at $250-$300..... but not much more than that.