Why buy a second copy? Just burn your first copy to a DL disc and watch that copy instead. It's only like $20 for a spindle of 10 discs and burners can be had for around $30. Sure, it ends up being about the same price as the box set, but you can use that drive to make backup copies of all your DVDs.
If you just want the movie, run it through DVD Shrink to get it down to a SL disc. Those only cost 20 or so cents a disc.