Here's a small curio. Using the Codices I own, and therefore the only ones I care about, what IS the bare mininum legal cost of an army? Let's find out, shall we?
Chaos Daemons
Herald of Anything Except Khorne, Probably Nurgle or Tzeentch Though
3 Nurglings
3 Nurglings
Total: 128
% of 500pts: 25.6%
As armies go, this is pretty bad. 20 Wounds is about all they have going for them. I'll have to do more of these for an idea of how good the percentage is.
Chaos Marines
Sorceror
10 Cultists
10 Cultists
Total: 160
% of 500pts: 32%
Better. One random power could work out alright. Could totally take the Daemons in a fight. Has 1 more Wound than the Daemons, but is less tough overall.
Dark Eldar
Haemonculus
3 Wracks
3 Wracks
Total: 110
% of 500pts: 22%
This is somehow worse than the Daemons army, with a stonking 8 Wounds of pain. At least they have more wiggle room.
Eldar
Autarch
5 Dire Avengers
5 Dire Avengers
Total: 190
% of 500pts: 38%
I thought the Eldar would be high. Still, they could totally cream any of the above armies, what with actual decent units somehow being their cheapest option. That said, I'd still be rooting for them even if I had to use Guardians instead.
Grey Knights
Coteaz
3 Warriors
3 Warriors
Total: 124
% of 500pts: 24.8%
As expected, this army is carried entirely by its efficient badass of a HQ, which is the only HQ entry so far with good offensive powers. Apart from the Sorceror, occasionally.
Imperial Guard
Company Command Squad
Veteran Squad
Veteran Squad
Total: 190
% of 500pts: 38%
The Imperial Guard are masters of cramming a lot into one slot. They also create a passable tax army, what with BS4 and Orders. They probably beat Eldar as the best army here until the Autarch finally gets into combat, but this comes at the cost of joint most expensive so far.
Necrons
Overlord
5 Warriors
5 Warriors
Total: 220
% of 500pts: 44%
It says a lot about Necrons that this is a significant improvement over their old tax, which was about double this. Comes with an AP3 firearm and actual anti-tank ability, but that does them little good in this context. Could be a contender, but likely won't be.
Orks
Big Mek
10 Boyz
10 Boyz
Total: 155
% of 500pts: 31%
Armed with shootas, the Troops here give the Dire Avengers a run for their money at first, but weaken quickly. They are, however, better all-rounders than the blue guys with stupid numbers of attacks on the proverbial charge. I'm gonna mark these as a contender.
Space Marines
Captain, Librarian or Chaplain (probably Librarian)
5 Scouts
5 Scouts
Total: 250
% of 500pts: 50%
This really doesn't surprise me. Bolters or sniper rifles on the Scouts, I reckon. Again, carried purely by HQ.
Tau Empire
Shas'El Commander with twin-linked flamer and blacksun filter
6 Fire Warriors
6 Fire Warriors
Total- 179
% of 500pts: 35.8%
The dark horse of the competition. Shas'El Deep Strikes and attempts to burn things, while Warriors try to shoot things. Could work, could not.
Tyranids
Tyranid Prime
10 Termagants
10 Termagants
Total: 180
% of 500pts: 36%
Doomed to failure. But still better than Daemons? Maybe?
So, who won? I'm leaning towards Guard or Orks, but maybe your opinion differs. I know it isn't an even contest, but forget about that.
Signing off...