I've recently improved my casting setup at home a little bit - I'm now using a jewelry mold vulcanizer for making my molds when possible. Its normally used by jewelry makers for creating molds for doing wax multiples, to support investment casting. Luckily the mold material supports low temp metals as well, so I can just dump pewter into it.
There are a bunch of these machines kicking around, since they seem to be quite indestructible, and they are also still being manufactured. It lowers my per mold cost, improves my process speed (1 hour for a mold instead of 48), and I get better results due to not having any bubbles.
I'm still doing gravity casting into the molds however, which seems to be the final hurdle in terms of quality. I've been looking around for a while a different solutions that folks have. This video by zombie smith miniatures (the guy that designed and sculpted quar) was the first thing I found. It seems to have quite a bit of setup costs, particularly the fact that he is using 9in molds for casting. This means that he had to build his own mold boxes. There are a few places to buy mold boxes still (contenti and spinbox both sell some that appear that you could chuck them in an oven).
The second thing I found was this article from 1966 showing how to build a 4in spincasting rig. The author is using RTV silicone, which I'd like to stay away from if possible. But the idea of mounting it on some simple off the shelf motor is pretty interesting.
This one using a washing machine as the motor and mount is pretty interesting - I'm not really sure how much the author is getting out of this setup. Maybe a bit, since you need to make your own pulley system to gear down an off the shelf motor if you go that way.
The final thing I found is someone from reddit that had built their own. No links because I've just been chatting with them, but they are doing a few interesting things. First, instead of making round molds, they are just doing little square molds like I'm using. The are also using something that is incredibly easy to build.
The idea here is that you have a bar with a central pivot, at the end of the bar are little carriers for your molds. These are attached to the bar via hinges, so that when the bar comes up to speed, they tilt up.
So to use this, you pour the molds with the whole thing stopped, then spin it up to speed (by hand! motor not necessary, though it is a nice process improvement), and keep it spinning there until your casts solidify. I am super into this solution. And the results they were getting were amazing. So I'm going to build one. I really like the fact that it can be done with mostly stuff from the hardware store.