I would defiantly consider the BluRay option because
1.) The quality is STUNNING
2.) I own Sleeping Beauty and Snow White on BluRay, and it is not blurry at all, you can see the lines that the outline the characters with and i thought that was really cool, and especially in a computer-generated film like UP would look wonderful on BluRay.
3.) The cost issue is not that bad either, i get all my BluRay Movies from Wal-mart. Wal-mart marks down the price by a lot, i probably saved more than $80 on my BluRay collection