Casting costs are nothing compared to sintering powdered metal. Printing aluminum comes with significant additional challenges too.
Investment casting tooling is expensive, but sand casting tooling is not and can be made from a multitude of materials. 3d printing not required.
For something the size and complexity of an intake manifold, tooling quotes for low rate (<10 parts) have ranged from $2k to $10k - depending on how much engineering is required from the foundry. From there, casts are probably in the $80-200 range depending on the level of complexity and processing. Then one needs to get it machined.
The last time I printed metal, I got about a dozen key-chain sized items for about $9k.
