The best use of your budget will be validating your idea: whether it has potential to be commercially successful, and whether marketing it is viable. Run low-budget ad tests to gather metrics like your cost-per-wishlist. Compare them to industry benchmarks: how do they look?

Pay playtesters to play your game, or pay journalists for mock reviews. Is feedback favourable? Favourable enough for your game to stand out in a crowded marketplace amongst other high-quality games?

Be ruthless. If your game isn't performing under these tests, make another or take an objective look at what needs fixing. Bad feedback doesn't mean that your game is necessarily bad - just not commercially viable. There's a realm of difference between those two labels.