I wanted to suggest a pair of alternatives for this:
- Using the total cost of your Mech's build (base chassis, OmniPods, armor, weapons, engine, etc.) in C-Bill value with non C-Bill Mechs being given a value appropriate for their stats when compared to sibling Mechs (I imagine there might already be a number to work off of as many of those Mechs do have a sell value. Balancing by C-Bills would justify making Clan tech closer in power to the BattleTech lore and be easier to implement as the numbers are already in game. The downside to using C-Bills instead of a Battle Value system, though, is that it might exacerbate the light Mech problem. So this might still be an imperfect solution.
- Implementing a Battle Value cost like in tabletop, but putting a battle value on each Mech and all the parts. Instead of using the Tabletop BVs, though, I would recommend rating them based on their effectiveness in MWO. This method has the advantage of being able to account in PGI's added quirks to ensure that certain Mechs are much higher value than similar tonnage counterparts.
I would like to suggest these values be used for groups as well, letting the team budget their group's cost the same way they have to budget tonnage right now.