So what did you go with?
And to everyone else I am looking for a solution, watcha got? 
I bought Hoagie_one's 128Mb card (link above). For PacketNES, it should be work fine. I'm not super enthused about parallel port and would rather have USB, but if it works fine (and I'm sure it will), I'll be happy.
You might be happy with pinballjim's Flash2Advance card which is nearly the same, but I think it's a bit older than the Flash Advance cards.
Alternately, if you have a spare CF or SD card, check out the
Supercard. I was very close to buying one of them. You can get them for like $45. I think the only drawback to consider is that a) they aren't 100% compabible for .gba usage, and b) there's a two-step save-your-game sequence. But for cheap 1 or 2 gigabyte storage option, it's hard to ignore.
Alternately, look at the M3 or another DS+GBA variant that you can move it to DS later on.
Tell you one thing, I'm dizzy from learning all about this stuff. I just wanted something quick and dirty for my kid so she could play Mario Bros.

-pmc