The cost of the Iron Works (IW) is quite small. For $600 and 150 War Supply (WS) you initially get 6 IWs. With War Bonds you can get the $600 at the cost of 25 Victory Points and -1% inflation, which is a good thing. Each IW produces $1 and 8WS per turn, and thus pays for the 150 WS in 4 turns (6x8=48 for 4 turns = 192 WS). The CSA can take D.C. from October, 1861 to late into 1862 even without the initial lost WS, so no problem there. The next cycle of IWs are also affordable. The catch is the location of the IWs. You can't hold everything and the cities with the IWs will be prime targets. If you must fight to the bitter end, the IW cities may end up in Union hands. Good luck!
I'm the 51st shade of gray. Eat, pray, Charge!