The problem is finding a moddable PSP from somebody that doesn't know may be more of a hassle than you're predicting.
I also had a PSP 3000 back on Christmas, but after discovering it wouldn't be hackable I returned it unopened. It was either that or wait to see if they _could_ hack them and do so any time soon. Let me put it this way: if I had kept it, I would still be waiting right now. It was a calculated gamble but one that I believe I decided correctly.
Moving from the 3000 to the 2000 isn't exactly downgrading. Many people are irate over some of the choices in them, claiming the graphics quality is actually reduced in the newer unit. Apart from the fact that the screen has an anti reflective coating, I can't find any discernible difference that I think would matter. The qualifier--at least for myself--is the fact that both the 2000 and 3000 had the memory upgrade that is supposed to reduce loading times.
After I returned the 3000, I put my effort into finding a 2000. I went to Craigslist, and the experiences were all terrible. The first time the guy knew nothing about PSPs, and possessed just the unit with a game. Everything about it suggested that it was stolen. The next person I contacted was suspicious about disclosing any information when I began asking about serial numbers on the unit and box, and anything else that might identify whether it could be hacked. I checked around a few Gamestops in California, and of the few I could find every one was scratched up and hideous.
So the way I see it, the motherboard type is another gamble and one I was unwiling to take, and end up stuck with an unhackable PSP. Unfortunately, you already made your decision when you opened your 3000. From my experience, finding a hackable 2000 in the private sector is a hassle. I've heard that the ones included in a specific bundle are typically a safe bet, if you can find them and are willing to pay for another brand new PSP. Otherwise I would suggest keeping an eye on the seller forum here, I just purchased a prehacked slim here and received a fair deal while others may attempt to charge a premium for preinstalled custom firmware, and it's up to you whether that's something worth paying for.