Hard to say without more info.
Price depends on what Vanguard model it is. Vanguard S1 or S2? Stainless barrel or blued barrel? Walnut or injection molded synthetic or composite stock? Used or new? What condition?
Consider ammo cost. I probably wouldn't buy a .300 WSM unless I was planning to handload for it. You can't find 300 WSM factory ammo for under $30 a box. Cheapest ammo you'll find is about $32 a box.
Honestly, if I was going to buy a long-range magnum rifle like a .300 WSM I would probably want a scope with a better reputation for quality and performance than a BSA Catseye. I'd consider buying the rifle without the scope. Take the difference and apply it to the purchase of a scope that will perform better at high magnification and under magnum recoil.