Prazon, alvarop is right. your budged is really tight so you have to specify exactly what you want to have... maybe a prototype of the prototype is doable for this budged...
- What does atacking mean, (range, close combat?
- how does the battlefield look
- what is the goal of the game
and so on...
if you have any fears that your idea is stolen (which seems like this is the case)
make your budget at least 10 times as big and then make an nda with the requesting developers