It would be nice to see the mechanical approach of an electronic guy.
Is there an reason to manufacture these prototypes in china and not locally?
May be a bad example, but if you change the fin direction it looks like a heatsink that could be extruded in long bars then cut heatsinks to desired widths.
That would be much more expensive.
Depending of the casting method the only machining needed is the contact-surface.
(Using a steel-mold or fine casting in lost ceramic molds.)
Using sand-castings the holes need to be drilled too.
For an extruded part you have to make the extruding-form, pay the setup-costs for extruding, pay the extruding, pay the set up costs of the saw which cut them in length, pay the cut, pay the setup costs of the mill, pay the mill costs.
All together this will cost nearly the same than milling the whole heat sink out of an solid block
Then just use one of those wire saws to cut that curve and drill two holes for the screws (use one big drill to remove fins around screw hole, then small drill for actual hole).
That would be two settings.
First drill the two holes with an stepped drill.
Stop the machine or let the machine work on another part.
Take the part out of the vice or holding device and turn it 180°
Put the part back & machine the second side.
Thats an quite labour intendsive work.
Thats why casting is the cheaper solution in this case.