In broad/general terms, the answer depends on how common your keyboard is, how much you are “married” to it and whether you are 100% positive that it is a simple case where you just need to replace the ripped off key caps.
For example, this site offers single keyboard keys for sale for an average cost of $4-$5 per key. Which seems like a decent deal. But just doing a casual check shows me that getting replacements for three simple keys on a MacBook Air (MD711LL/A) keyboard would run me about $27 and that is without shipping.
But then a quick look on eBay for a full replacement keyboard for a MacBook Air (MD711LL/A) shows me that I can score a whole keyboard for $23 without any additional shipping.
In the case of your specific laptop model—an Asus ROG G73JH-A1—a quick search on eBay shows that you can purchase a complete, brand new replacement keyboard for about $14 with free shipping. So in my mind, a full replacement keyboard is your best bet.
And in general—and even without knowing what make/model of machine you are on—I believe that purchasing a full replacement keyboard for a system will always cost less than purchasing individual keys. The nature of the way many keyboards are manufactured nowadays—small components, very little standardization and even variance in size/shape/layout within a model line—makes them essentially disposable commodity components.
So a full keyboard replacement is a common commodity that can often be purchased for less than individual keys. Changing individual keys is an anachronism at best nowadays and only seems to happen when one really wants to customize their laptop’s look or they are using editing tools with elaborate key combos that require a custom set of key caps.