Rally the troops at the moment gives a single AP to each soldier in the squad except the caster, no WPs, and it costs 2 AP and 4 WP and can only be used once a turn by each soldier that has it.
The exploit from this skill at the moment comes from having 3+ soldiers with this ability in a squad, because you are leveraging 6APs+ to get, in an 8 soldier squad, 21 APs back, which is basically like 5 soldiers getting a whole turn back… And if you bring 7 soldiers with rally the troops, it’s 49 APs back, which is more than the APs your squad started the turn with 
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But note that raising the WP cost for each soldier won’t really solve this problem, because each would use RtT only once.
The same thing happens with rage burst at the moment, because it’s a one shot killer, see the discussion here So... Rage Burst can no longer cover multiple targets most agreed that it should cost more WPs to use and some that it should drain any WPs leftover and all the APs from next turn, in addition to nerfing the damage output either by limiting the number of shots fired to 3-4, or drastically reducing accuracy. Ah, and @MichaelIgnotus and me really want the sweep back in RB with AW, which is basically the most important take away on fixing RB 
And this is the biggest problem I see with curbing exploits by tweaking WP cost, or recovery rate: it doesn’t eliminate many exploits, while it nerfs non exploitive uses of the skills.
To bring another example: mindcrash. A squad of priests with jetpacks and inspire. Mindcrash has 0 AP 6 WP cost. Using a jetpack and 2 mindcrashes (and give them a frenzy first so they can really move around): 15 WP and 3 AP for 200 damage ignoring armor to every opponent in 10 tile range. So square the cost of the second mindcrash to make it absolutely prohibitive: I don’t care, I have a squad of these guys. And every time they kill something, 1 WP back to everyone, to use on other abilities.
Bottomline: I think the solution is to address each skill as an exploit using it is discovered. E.g. RtT: limit uses per squad to 2. Mindcrash make WPs of opponents act as defense or give it diminishing returns. Discussed here Priest weapon exploit (this game just become much easier) - #6 by pantolomin Stealth https://forums.snapshotgames.com/t/lets-fix-stealth/8511RB, etc.
EDIT: typos