Do you really need a 16GB memory stick? Or, do you really need the entire series all at once on the stick? I mean, my Xbox has an 8GB hard drive, but I wouldn't throw an entire series onto it, simply because it takes up a lot of space and it's not like I'd watch the entire thing in a very short space of time. Unless you're going to plough through episodes at, like, eight a day or something ridiculous, I think just putting a few episodes on at a time would make more sense - the .ogg versions of Jetters I have are only 70 to 80mb each, so you could theoretrically stick half the series on a 2GB memory stick (though I don't know if the PSP can read .ogg, it probably needs converted to something else which I guess would be twice the size).
And judging from Amazon.com, the 2GB memory sticks are only about $5.50, so even if you got two or three of them it'd definitely be saving a lot in comparison to the 16GB memory stick that sounds like, after you'd watched Jetters, wouldn't get a lot of action afterwards. Then again I'm pretty clueless about the PSP, so I'm probably talking nonsense.