you can pick up a 3Tb external for
$120USD
The pricing of that drive is a bit strange. $7ish difference between the 500GB and 1TB, $10 per 500GB after that until you get to the 3TB where there's a $25 jump.
Not much more to add to this thread, though, other than to say... No, nothing, just buy a 250GB hard drive, back up your PS3 on it. Oh, maybe I'd recommend: A USB stick in addition to the hard drive for the saves that can be copied, because not only can you never have too much storage, you can also never have enough backups, and buy a hard drive SPECIFICALLY for backing up your PS3 and nothing else at all, ever. I say this because imagine this scenario: You go to copy some files from your computer while your PS3 is doing something. You have a power cut, your hard drive gets corrupted, your PS3 gets corrupted, and you have no other backups. Stuff like that can happen, trust me.
Oh and don't buy Buffalo drives, I had a 1TB drive I used to back up my computer, Sod's law dictated that my girlfriend should also back up her stuff on my computer, and then one day when my computer was automatically backing up I noticed that the backup made no progress in half an hour, when it should have taken a few minutes. Upon closer inspection the only bit that Buffalo had actually made, i.e. the USB to SATA interface, had died, and with it all my data and my girlfriend's, whose laptop had, I kid you not, died the day before. It took a
long time for me to recover from that one, I can tell you. My data was fine, though, because my computer was also fine.
So as it turns out, I did have something to add.