You can plate with any non copper based alloy, many use nickle. All
you need is a decent flash, so even if you use gold, you’re not
really putting that much on.
You can also use layout fluid like Dykem, available at any machine
tool supply place. It leaves a slightly thicker coating so it can
fill in very fine, high detail pieces a little, but it’s easier and
faster for the right items.
By using silicone molds you can bypass the issue entirely, they cost
a little more in materials, but will produce good castings faster.