I'm currently on the fence with going triple screen. While I think it would be very nice (I have trackIR equivalent and think it would be great on 3 screens) I'd have to factor in 3 new screens, something to mount them all and a pretty hefty GPU to run them all at a decent framerate. That would probably come to around £1200, assuming £200 per screen, £500 for a top-end GPU and £100 for a decent mount setup).
I'm tempted now instead just to get a nice big 27/29" IPS panel and just run 1 screen well like the last poster describes. Probable cost would be 1/2 the above and if the screen fills my FOV it'll probably be immersive enough.....