A realistic solution for no numbers is to do something like the Braille system and reuse the letters from A-J as numbers, and then use Arabic notation, not Roman. I believe Hebrew also did something like this. You'd add a notation to indicate "this is a number". Braille basically uses # in front of all its numbers, although currency signs and a couple of other things are considered "obvious". So $EAB.IE is $512.95.
What really bothers me is the omission of rather more fundamental stuff, like punctuation, mathematical operators, how the text is emphasized, or instructions on how things are even written (right to left, up to down, in any random direction that looks pretty like with Ancient Egyptian).
But then you fall down the con-lang rabbit hole, and for that it's easier to just say your Orcs speak Klingon, the Elves speak Tolkien's Elvish, and Dwarves speak Esperanto. Or German, Mandarin, and Swahili.