What you are asking is a fairly generic question for a specific issue, as Keycaps and Key sets are VERY specific.
We provide custom printing and blank keys, caps, and sets here.
Give us more info and we would be more than happy to see what can be done for your particular project. We are currently checking on blank sets for the HHKB Pro, black and white.
How much for a set of blank black keycaps for an alps siig minitouch kb1903? lol It has half function keys, and a weird tab key with a piece of plastic covering an open space, can you make keys like that? Alternatively, how much for just a set of black blank keycaps for just the letter set and possibly the spacebar.
The ultimate would be all black, with red keycaps for the function and escape key, with black lettering. Then the board would have all black blank, except for the special keypad which would have the pgdown, and function modified number pad which would be black with red printing on them. Just the pgdown, arrows, and number's, still no letters. Also the function keys and number keys would have red printing on them.