where can this be purchased
Where can I purchase leopard 10.5?
Mac OS X (10.5)
call Apple Store ( they have some dvd sets but only if you ask for it ) or ask at your local Retail Store ( unlikely they have it )
Estimated price for new was roughly130 US$ // € . They don't get cheaper only becasue they are old, be prepared.
The update to 10.5.8 ( the last major nugfix update ), iTunes 10.x, Safari 5.x is free, comes via SoftwareUpdate or can be downloaded via Apple.com/support download site