It’s really difficult there is easily too many factors here. To name some;
Programmers experience, Experience with the Engine, Experience with Multiplayer/Replication fundamentals, are they available full time.
I think Andrej J. is right. It seems this question is to work out if you have the correct funds. I think you need to separate the tasks into goals and work out the cost per Goal.
I.e
Fully replicated Character Movement and Actions - X amount of £
Child classes for Medic, Soldier, Spy with functionality - X amount of £
Weapon and projectiles - X amount of £
UI/HUD and Menu’s - X amount of £
Doing things this way has benefits like the below,
Programmers will get paid by Milestone (goal). Programmers will work faster to get the reward to complete work and essentially get another contract etc…
You can visually track the progress and present this to your investors.
You can split goals per programmer. You may choose to give your most experienced Programmer the biggest goal (which pays him the most when complete) and give the easier tasks to your less experienced programmers.