1. More money for a qualified instructor - I would present the marching competition sheets showing that color guard has been an issue in the past competitions and that the addition of an instructor is necessary to be competitive at the 5A level in your region. If they are unwilling to hire a person as a para that can do that, present them with a number to increase your clinician budget by. Back when my program did it, we paid $1200 a month for the color guard instructor. You also need to point out the different costs associated with color guard as opposed to marching instruments. You may have more of a leg to stand on if you have a separate "marching instrument" repair budget already.
2. A separate budget item - I would present this as helping the school board ensure that "the cart doesn't come before the horse." If they were to create a separate budget and only let guard expenditures come from that budget they can ensure that the color guard does not take over the rest of the total band program. You may shoot yourself in the foot down the line with this one.