Here's the kicker. The i7-3770 will be the best option. The i5-3470 is the cheapest option, the i3-8100 is the best for just that game, but far more expensive overall as it'll require not only a new mobo but new ram as well. The i3-8100 will handle GTA:V, but is no better than any other 4 core/4 thread cpu in that regard, the i7-3770 having 8 threads will do better having a more consistent fps.
An i5-8400 would be the absolute best, but again is far more expensive overall than a simple cpu swap.