I wouldn't settle for one that needs a lot of tlc (500-600), you should be able to get one ready to go shoot for that money. I would go with the .300 imo.
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I agree with Texken...
For $500 and most certainly for $600-$650, you should be able to find a Model 99 "EG" in .300 Savage that is in 90% or better condition... a rifle to be proud of and that will shoot very accurately. You definitely should get a .300 Savage rather than a .30/30 because the .300 Savage is ballistically FAR superior.
Model 99s are "THE" most accurate lever action rifles ever made and should shoot 3-shot groups of less than one minute of angle (1 "minute-of-angle" = 1-inch at 100 yards) rivaling many good bolt-action rifles. Of course, this assumes you have a good scope (a 3x-9x 'scope or stronger) on your rifle. You can't shoot better than you can SEE!
The "99's" excellent quality, fine accuracy and outstanding reliability are well-known among those riflemen who know about such things.
If you don't hand-load, you might consider starting to do so since factory ammo is getting very expensive and you can load-your-own for about one-quarter of the cost of factory ammo plus you can "work up" a much more accurate, somewhat higher velocity load by hand-loading than any factory load will give you.
Keep your eyes open and keep looking around.. you're SURE to find a good Model 99 in the $500 to $650 price range. Some members have even found such good rifles in the $450-$600 price range. Prices vary considerably around the U.S.A.
Look at estate sales and in pawn shops. "Talk-it-up" among other shooters at the rifle range... tell 'em that you're looking for a Savage Model 99 in .300 Savage caliber which is in good condition... they're out there, you just need to FIND 'em!
Some members in this Forum may have a Model 99 they're willing to sell... so don't give up.
Good luck in your quest... and let us know when you find YOUR Model 99...
Strength & Honor...
Ron T.