Is an osx restore disc the same as an install disc?

So i have a iBook g4 (A1054) it meets the system requirements for the installation of osx 10.5, as I am currently running tiger which as many of you know is severely outdated. The only problem is, is that i need to find an installation disc. I need it to be under 20$ and i've looked on ebay and the only ones i found are all "restore discs and software discs" while all of the others are like 80$ which i cannot afford. So are they the same or not? And do you know anywhere where i can buy a leopard disc? Like from apple or something..

Thanks.🙂