https://wiki.stararmy.com/doku.php?id=list_of_general_melee_weapons
The booster here lists it's price as top engine speed (CC) x 20. But that can't be right, because CC isn't a measure of even horse power or such, it's a measure of cubic centimeters of the pistons, it's related to the power of the engine, not the top speed.
So I can only see three interpretations of this
1) You meant CC, but if that's the case, then the x20 makes it prohibitively expensive, as decent CC ranges from 150 (thus costing 3000) to 600 (12000) for that booster (this is using motorcycle engines).
2) You meant C, as in the speed of light and it was a type, but since you specifically mention not being able to use FTL or other fantasy engines, I can't see that as being right either, not to mention it has the price cost problem of 1, only in reverse (as even going 0.5 C, and thus striking with the force of several dozen nukes, would only cost 10!)
3) It was meant to be speed in either kmph or mph, and the CC was a mistaken thing.