I have a slim 2501B 320GB for sale. I bought it brand new back when they were being shipped with 3.50 and only the 3.41 jailbreak was available so I had a friend of mine dig through the boxes at the store he worked at and find me one, based on the receive date, that was on 3.40. The console had 3.40 and I updated to 3.41 and ran that for a while. Then the whole 3.55 thing started and I updated again. Later I decided that I wanted PSN and updated. A year or so later I decided that it was a mistake and got downgraded through a person on this forum. Currently it is on Rebug 4.41.2. The console is not banned. However the day received it and stated playing and decided to move it when warm my screen went haywire (I am in no way suggesting that it happened when it was being downgraded, I think it was a freak coincidence). I made a thread about it here and was sure something was up with my GPU. I found a good service locally and got it reballed. I stayed and watched while the person did it in front of me. The solder was in a horrible shape, I have no idea why. The console has 50 hours played total in 30min-1hour intervals 90% of which from games on the HDD(probably less than 50 but I am saying that just to be on the safe side).
So basically what you're getting is a reballed, downgradeable, smallest technology (45nm CELL and 40nm GPU) slim with a 320GB HDD. It still has 11 months warranty on the reballing. I got my sister to play Sims for a few hours this week to make sure it doesn't overheat or develop any GPU related issues. It is in almost pristine condition other than a few (not many) scratches on the sides. It includes console, power cable and the power switch I've bought for it. I can include a controller if you're interested and we settle on a price. I am located in SoCal in south Orange County and I encourage the buyer to come and test it. I am asking $300 for it.
Here are the pics: