For $1500, I'd say spend half on the rifle, half on the scope... the best of each that you can find. For $750, you can get one heck of a decent bolt action rifle, and a fantastic scope. Too many choices to list here... Once you get into that price range, they're all pretty good and will only be personal preference.
As for caliber, 500 yards isn't that far for most bigger calibers, but for hunting it is. As far as the rounds that will reach that far, with decent trajectories, in normal calibers, and enough oomph to take a decent buck, I'd say:
.270
7-08
.308
.30-06
7mm mag
The 7mm probably has the best trajectory (least holdover), and carries the most velocity/energy/momentum at that distance. The .270 has the next best trajectory, and is 2nd or 3rd in vel/en/mom (depending on which .30-06 is being used), with the .30-06 being 2nd or 3rd and the 7-08 and .308 about tied in all areas in 4th/5th place.
If it were me, I'd go with the .270. It has less energy at close range (but still more than enough for deer), but holds it's energy better than the others at long range, besides the 7mm mag. The 7mm mag has the higher recoil that could affect 500y shots, and is probably too nasty at close ranges, making close shots less productive.
There are plenty of other good choices, but I see little reason to go with them at their price (and low availability) and only 500 or so yards of shooting. These would include most rounds .257 mag (not Roberts) and higher. Of note... .300 mag, .280, .338 fed...