Assuming Exactly 5K forces should give you 8182 BV in Combat Unit BV + 1818 BV in C3 Network + Link Fee.
I've got that coming to 454.5 average cost per unit.
The same 8182 force as a single force of linked C3 would cost 1636. So agreed a little more expensive Joel's way.
But, if 3 forces link up its also cheaper.
Triple 5K force = 12273 Combat Unit BV + 2727 C3 Cost as 3 separate teams w/ the 10% link fee.
The same 12,273 Force linked as 6 units would cost 3682 BV for C3 link.
Unless you are working off different assumptions your numbers cannot be right. Giving a BV total of 10,000 the average unit cost will be 2,083 each for 4 units for a total unit cost of 8,332. Take 5% of that to get approximately 417 BV per unit surcharge. Add 2083 + 417 = 2500. Multiply by 4 units and you have your 10,000 BV.
Also, the flat fee is more expensive than paying the actual costs. In the example above each player with 2 units each would pay 834 BV for their half of the network (417 BV / unit) for a total of 1668 BV in C3 costs. Using the flat fee method my actual costs are cut in half because I'm just linking my 2 units but I have to reserve 500 BV to link with the other player. By the same token he has to reserve 500 BV to link with me. Assuming 2 units each and spending the max possible on units (no skill upgrades) each of us can spend an average of 2,045 BV per unit with a surcharge of 204.55 BV per unit. That means the 2 of use are paying a total surcharge of 409.1 + 500 = 909.1 BV each to link our forces for a total of 1,818.2 BV.
That means we are paying approximately an extra 150 BV total (75 BV each) using the flat fee method under these parameters. It gets worse too if one player decides to divert points towards skill points or non-C3 units as that means his C3 force is cheaper but you are still paying 500 BV. It also gets worse when you add more players though I am assuming each player has to pay 500 BV for each other player in the network. Under that scenario each player would have to pay an average of about 1,364 BV (or 210 BV extra) using the flat fee method over calculating the actual costs. If each player is only paying a total of 500 BV regardless of the number of players in the network then yes, the discount would be about 250 BV per player rather than a 210 BV deficit.
Using the flat fee method is not a huge increase but if you already thinking you are paying too much for C3 then it could be a problem for you.
Agreed on the Non-C3 units part, but, I'm not sure what you mean by the skills part. Skills affect the C3 cost, or C3 affects skills cost, I forget the order but the end result is your paying the skill multiplier for the C3 so it should be the same %.
Order of operation for calculating the BV of a force is TAG first, C3 second, pilot skills third and finally FSM if used. So as I mentioned before skills only affect how many points are available for the base force but does not directly affect the cost of C3. If I had 10k to spend and I want to use 1000 points on skill upgrades during skill assignment then I can only spend a total of 9000 on the actual force including C3 costs when building the initial force.
Note: If anyone see anything that looks like a mistake just let me know. I'm pretty sure my numbers are correct though as I've been playing with them for the last couple days.