My first thought is to stop shopping at Gander Mountain, you'll save $50-$150 on a rifle. And yes for the most part I believe that good glass starts at just over $300. But, I have had good luck with two BSA scopes. Both of which I got on sale for less than $100. They are more than adequate for hunting. I have had bad luck on two NC Star optics.
Second, I would choose the rifle then the caliber. Any medium game caliber will work for whitetail and hogs. For a brush gun, I'm thinking that a 20" is right, so some cartridges that don't work as well is short barrels should be eliminated.
If this will be your do everything rifle, and 25-200 yards is your range, then there are several great calibers that work well in 20" barrels... .308 Win, 7mm-08, 6.5x55 Swede, .358 Win, .35 Rem, .30-30, .308 Marlin Express, .338 Marlin Express