Herpluver,
Sounds like your heart is in the right place however... A Savannah monitor is a good choice for a beginner monitor there are many things to consider about the long term care of such a large lizard. Savs usually don't grow much longer than about 3 feet total length, however that still translates to having an enclosure for an adult of the minimum size 8' x 4', preferably larger if possible. They are largely insectivorous in the wild and should be fed a diet that matches that preference which means loads and loads of crickets, roaches, superworms, etc. This diet can be supplemented with whole rodents but rodents should not comprise the bulk of the diet. You can find pretty much the best, most up-to-date information the book, 'The Savannah Monitor Lizard: The Truth about Varanus exanthematicus' by Daniel Bennett and Ravi Thakoordyal. The other point to caution you about is the inevitable vet bills. Pretty much all Savs available are from wild-caught stock that has come straight from Africa and likely has never seen the inside of a vets office. I currently am treating a juvenile Sav I adopted from my local herp society. Over the 3 vet visits I've had already I've spent in the neighborhood of $180 and I still have another fecal check/analysis coming this Friday which will cost another $40 in addition to any further medication that may be necessary. Bear this in mind.
Best of luck,
Matt Campbell