It depends on what you think "Cheapens" your victory.
If you level grind on victory road, it will take a longer time. Pokémon levels there are in the 30s-40s, and you'll need to spend some hours grinding. The way I see it, this way is the least cheap way of grinding up to the level of the Elite 4, done with honest work and effort. (And many trips to the Pokémon Center.)
If you use the MissingNo. item duplication method, you can easily get to the level of, and beyond the Elite 4. However, using rare candies to grind is cheap (you said so yourself) and you'll miss out on some evs if your team isn't already maxed out. This doesn't seem like a good option to me, because it cheapens you victory, like you said. However, if you're fine with cheap, feel free! I wouldn't recommend to though.
Like sumwun suggested, you also have the option to grind on the Elite 4 themselves. This is the fastest method, and you may actually beat them while grinding. The Elite 4's levels are in the 50s and 60s, but your Pokémon have evs, so you probably stand a chance against them right now, just buy a lot of potions and revives.
However, I don't know your definition of cheap, so if you consider rematching the Elite 4 until you beat them to be cheap, just grind on victory road instead. I would recommend grinding on victory road, or the Elite 4 depending on what you want. Either way, it shouldn't take too long to get your team to level 55-60, and then you should be fine.
Good luck! I hope I helped!