Why not just allow complete customization? Let the sponsor chose how much of what they want to pay from the war chest. It would certainly make some armies more desirable than others. Besides, this is a broad stroke thing. If the sponsor wants to pay fro 100% of recruitment, they will be paying for the neighboring dukes SF's if he is in the army as well as the new knights awesome archers.
Recruitment: 0-100%
Training: 0-100%
Repairs: 0-100%
Travel: 0-100%
