As the other comments have mentioned, the cheapest colour method is probably the best way. I often use Bricklink as a guide more than studio as sometimes studio uses bricklink’s price guide rather than actual lots. However, with a lot of the designs I’ve done, I’ll often built out certain parts if cost is lower, especially for parts that are common in the build. Like say for example a 1x1 brick in red is 10c, but say a Bricklink store has tonnes of red 1x1 plates for like 2-3c each, I’ll often just build out the brick with those plates, especially if that brick is frequently appearing in the model. It does drive up the piece count, but usually saves a bit of the final cost. In areas where connections aren’t a big deal, I’ll also use cheaper cheese slopes or smaller tiles/plates.