Guess it depends on why you want to get rid of it.....I agree the .30-30 and .223 are probably the cheapest to shoot....however the .35 and the .7-08 , are the better and more effecient rounds, at least in my opinion. ( assuming you handload , if not my opinion may vary ) I also agree , a .22 rimfire of some sort would be a nice addition. To answer your question..I'd get rid of the .30-30 and buy a .22 rimfire , 12" would be my choice. A 2-6 Trophy on it , a dandy squirrel outfit.
regards , irold