You can find a lot of CFW-able PS3s on eBay for anywhere between $150-250, you MUST have a PS3 on or capable of downgrading to 3.55, see the SKU model link I posted above for a list of which models do.
It's best to simply suck up the price and buy a 3.55 PS3 on eBay IMO, it ends up being easier than buying a correct model PS3, downgrading if its not on the right FW/sending it off to be downgraded. You can simply search for 3.55 PS3 to find hackable ones.
ODDEs also got screwed with the 4.55/4.60 update, so you'll also be stuck below those firmware if you choose to go that route, I don't think any of the ODDE makers found a way to bypass it.
EDIT: also, you will NEVER find a new CFW-able PS3, you'll have to deal with used or none at all