Personally, I wouldn't bother w/ cam/carb changes for mpg. It's a lot of money for very little gain.
My suggestion would be:
Change out the muffler for a better/less restrictive one. The stock muffler is VERY reastrictive. Restriction does not help effeciency and that's what you're really after.
Next, tune that carb within an inch of it's life. Leaner doesn't always make for better MPG so don't just go putting in tiny jets. You'll do more harm than good. Also, for steady cruising you will mostly be using the pilot jet so that would be the place to look for mpg as well as the needle setting. The main jet doesn't come fully into play until you crack her open and changing it will only have a very small affect on small throttle opening riding and MPG.
After that, re-gear. The Savage is hopelessly short geared. It may take some experimenting to find the best gearing for mpg. Gearing too tall will make the motor struggle too much and hurt MPG, too short will cause unnecessaryly high rpm's. A chain conversion is pretty much the only way to accomplish the gear change. Sprokets are fairly cheap too so buy a few different sizes to experiment. The front sproket will make bigger changes and their VERY cheap (last one I bought was like $10) so I'd start by messing w/ it first. You can "fine tune" your ratio w/ the rear sproket which will make smaller ratio hanges and cost more.
Lastly, adjust your riding style. Use small throttle openings to accelerate. Keep your speed down to the speed limit or whatever you can get away w/ without getting ran over. Pull in the clutch and coast as far as possible to stops. Just letting off of the throttle w/ the clutch out isn't going to net you good MPG. The RPMs are still up and the engine is sucking in fuel. Letting it drop to idle and coasting uses VERY little fuel and because you're still moving MPG will be VERY high during this point. This will help boost your average MPG.
I don't think 70+ MPG is out of the question w/ the Savage. I have an 883 Sportster and on a recent day trip I averaged 60mpg w/ that thing (over the course of 3 tanks). My Buell XB9S would consistantly get me 55+ MPG when I had it (so long as I could stay out of the throttle
) A small motor isn't necessary for good mpg so there's no need to go to a 250. A well tuned machine can get great MPG if you ride it right and make the right changes.