So, I've been looking into the possibilities of the field of custom keycaps and I first decided to tackle the big one of actual new keycap molds. As it turns out, Signature Plastics will usually charge you about six grand per mold (ABS double shot machine variant). Of course, most people choose standard letters with some legend changes instead because doing that is way cheaper than doing what I'm suggesting and anytime someone wants a custom key like that...well...you just get an artisan type on the phone and put in an order.
However, there may be a better way. See, the pricing information of custom molding is something I had to call SP in order to get. While I got them on the phone, I also asked them if they would be willing to take other people's molds and use those in their machines for manufacturing. They said that as long as you can meet their specific engineering standards, they would take in the molds and use them. Now, I didn't get as far as to ask them what those standards were because I haven't gotten that far into the process yet but now I know there is a way. Besides, you can get a generally good picture that it would require material and measurement specifications around the same as the rest of the industry so steel molds that fit within a specification of about a hundredth of a millimeter.
This is all easy enough on paper but now comes the task of finding a cheap enough method of making such molds with those kinds of specs. My best guess as to what would fit would be SLS printing or Selective Laser Sintering printing for all those in need of the full name. Effectively, this can be summed up as metal 3D printing. If anyone else has any better ideas as to how to make high quality molds for cheap or where to get such services in the 3D printing world I'd like to know. I've got some contacts and sources as to where to find these guys but I'll need to dig that info back up so it'll take me a while. Regardless, it should be fun.