For about $450, you can get a Leupold VXII to put on your rifle. I have a VXII and a VXI on a couple of rifles, and the VXII is a clearer, brighter scope (not that the VXI is bad or anything). The Rifleman and VXI line have friction windage / elevation adjustments while the VXII scopes have click adjustments and better lens coatings. The friction dials work, but I much prefer the "click" adjustments.
The Bushnell Elite 3200s seem to be popular with a lot of hunters too, but the Leupolds offer a little better eye relief, which might be something to consider with a .300 mag. There are a lot of scopes in your price range that you could look at including Burris, Weaver, and a few more, but Leupolds are serviced in Okotoks. In the unlikely event that something goes wrong, you won't have any hassles getting it repaired.