Osx 10.5.8 pt mp7.4 - osx 10.6 pt 8?

[FarmerG]

Hi everyone, I've been trying to figure this out for a while now, so please forgive me if this HAS already been answered :/

I'm running a 2008 model MacBook, running 10.5.8 and Pro Tools MPowered 7.4.

I backed up my computer today, and went to the original discs, to erase and re-install 10.5 as my OS was starting to lag. Turns out the first disc is bust, and I can't get another one because they're out of print.. so I've had to update to 10.6 (discs will be arriving soon).

Now, I've just found out that PTMP 7.4 doesn't work with OSX 10.6, and I have to upgrade to PT8 (MP?) for it to work once I have a fresh, lagless machine.

..can someone *PLEASE* tell me if there is a place I can upgrade at a cheaper rate? I saw a deal some time ago saying you could get PT8 cheaper when upgrading from 7.. but the website isn't exactly the easiest to navigate... and with a 17 month old child running around... I'm starting to stress!

Many thanks if anyone can help. I can't afford to spend a ridiculous amount of money... so I may have to revert to downloading a fresh 10.5 disc instead of upgrading to 10.6 :/