One of the more amusing entries in the civilization series was the unit explanation for mechs. The idea was that while they wern’t actually as useful in battle (high profile, more complicated, etc) as more conventional units but served a ‘cool’ factor that attracted funding for more effective but less showy war materiel.
Maybe you could use this idea. That is if you include 'mechs the entire force gets a discount because of public / political perception that this battle is important. After all, the mechwarriors are being sent in! The more mechs the bigger the discount, but then you, the general have all these damn ‘killer robots’ to somehow use!