I'm certain such a mechanism exists, but I would suggest that
1). The Hull-Damage value calculation will be highly nonlinear.
2). The effects of 2/90 and SM will be a huge void for exploitation, as the combat value is also massively dependent on the quality of the weapons array
3). GEG values will be very difficult to judge
4). Don't even get me started on trying to conceive of the values of the +1 Rangers/Vree crew quality bonus
A correct formula is probably so difficult it would make my head hurt. Triggy's calculations would be a start, but I guarantee once people actually see the formula, the ride pimpage would start, twisting the balance in it like the One Ring destroyed Smeagol. It's what we, as gamers, do -- it's called "powergaming", and there are lot of 'em out there.
And it would damage the whole point of the Priority Level system. Even if you don't like it (and would rather have points), it's positive argument is that it maks buying a fleet super-easy. Now, building your fleet and verifying your opponent's could be a process longer than Car Wars. Yeek.