Psst ! Here's a little tip for you. The drive used in Mac Pro's isn't exclusive to the mac. It's an Optiarc model
and I believe you can use any cd/dvd burning drive with an ATAPI plug on the back, Pc or Mac, and chances are it'll work fine, I used a Lite-On drive I snagged from a dying PC in my Mac pro 3,1 as my 2nd dvd drive
and it worked fine for a few years. Replacing it isn't that hard either. There are guides on Youtube or other places that show you how to do it. Just remember to remove the little lip on the front of the dvd drawer before you install it. I don't know about specific brands, but Pioneer seems fine, and I'm sure there are others that are fine, too. macsales might help you out. I know what it's like having to haul your Mac pro into your local Mac place--a pain in the butt, right? and then you have to wait...and wait...
I think you can can do this....
good luck
John B