Get a cattle trough. Can't beat those for housing. Monitor lizards need a very think soil as substrate. 2' soil depth minimum would be great for a savanah.
Why did you decide on a sav. monitor or nile? I figure it is because they are the cheapest of the monitor lizards.....they are only available as WC or CH.
Do yourself (and the monitor) a favor.......study monitors intensely, decide which monitor you would like to keep, setup the appropriate housing, then get a quality CBB monitor lizard. Ackies would be a great lizard to start with if you are really interested in getting a quality monitor lizard......lone males go for around $150 each and can be great to keep ;)
Thousands of people buy savanahs and niles each year......ever wonder why you don't hear of too many people that have had them very long??