I do not know what guns you have, besides the model 99CD. Is your 99CD a 308? I do not know your laws, does the Model 24 count as 1 gun or two? If one gun, then you not only get a 30-30, but a 12 gauge shot gun as well. If they count as two, then I would pass. If I was limited to just 6 guns, I would be sure to cover as much ground as possible with each one. I do not have that problem, I have more than 6 guns that are in .224 center fire alone, but If I was to only have one, it would be either a 222 or a 223. I would make sure there was as little overlap in guns as possible. Like a .224, a 6.5MM or 7MM, a .308 (30-06 or 308) and a .358 or .458 and then a 22 rim fire and 12 gauge shotgun to make up my 6 guns or something similar. But that is me. BTW - I think $200 US is a good buy for a Model 24.
Let us know what your decision was.
Good Luck and Good Shooting