You don't need 2s2p lipos. You can do fine with a simple 2s1p or 3s or 4s or whatever you need, in the 4000-5000+ mah range.
the only reason you need parallel packs used to be to get more amps/capacity in the old days with 2000-3000 mah lipos. I think. Most lipos today are good for 15-30C and 4-5000 mah.
The cheap good stuff as far as lipos can be found at hobbyking.com. Look for Turnigy, Zippy, or Rhino (though Rhino's tend to be longer, like a 7-cell nimh). They usually have the popular lipos in stock if you know which ones to look for. I just saw several hardcase packs in the 4-5000 mah 2s range raged for 20C for $20 on there, in stock.
Here's a few links:
[link=http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=8357]Zippy Flightmax 2s hardcase 4000 mah 25c[/link]
[link=http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10098]Turnigy 2s 5000 mah 20C hard case[/link]
Or try searching for "hardcase" and that'll bring up a bunch. You DONT need hardcase, but those happen to be in stock, and are the exact size of a 6-cell as I understand. Other in plane shrink wrap can be a little thicker or a bit longer and may not fit certain cars with only 6-cell Nimh space.