By e3 flashed, that just means it was downgraded, right?
I have 2 jailbroken PS3s and handled both of the purchases differently.
When I my PS3 slim, I paid someone to do a downgrade on it. It cost me maybe $300 for the PS3 + Downgrade, but it came with a bunch of add-ons like 2 move cameras, the TV Tuner box, DVD remote and a bunch of games. The stuff I didn't want I managed to re-sell and got some of my money back.
With my second, I bought a 60gb US model which was never upgraded from 3.55 (warranty sticker was still in-tact), and it had no YLOD or problems. The unit cost me around $250 I believe, which seemed like a steal for a launch 60gb model which never had YLOD. I just did the CFW installation myself. I did send it in to Endless Electronics for some work on it to help avoid YLOD in the future, like fresh heatsync, fan mod and stuff. I think it cost me $100 including inter-state express shipping to them and back again. Was about as much as if I'd done the work myself, with none of the risk.
So if you are really in doubt or concerned about the state of the PS3, you could try looking for a 3.55 PS3 and just do the CFW yourself. On ebay, a 3.55 slim seems to go anywhere from $200 to $300. A fat seems to differ in price depending on the model, condition and whether it has had work done to it, but it's a real gamble if you don't know what you are looking for. Although if you don't care about the PS3 functionality, a slim is fine.