I'm gonna start this thread with a discussion regarding the Exp transport cost.
Comparing it to the t3 uef transport, it can transport 3x the units at t3, and also has 5x health.
So taking upper of these two, 5x mass cost of t3= 7000
Adding the cost of air fac upgrades that comes to about 10500 mass
Then there is the torp capability for that dps you need roughly 1500 mass worth of torp bombers. (t2)
=12000
Then theres still the aa capability and exp transport to account for, which I will approximate to 4000 mass.
Total 16000 mass at this stage. Of course this is very rough, but I think would better price the transport than it is at the moment.
Comparing this to the Czar at 45000 mass- it may seem very cheap. But put a beamer on the comet and the two units become quite comparable. 3 comets with beamers have similar direct fire, aa, health, and mass costs.
The comet would however have more torp dps, and the ability to drop into enemy bases as well as being used as a ghetto gunship vs the czars factory.
Considering this my final reccommendation would be bring the cost down to 18000, possibly with a view to lowering it further if thats too much still.