I see no problem spending an additional minute on scene to get a twelve lead. If bleed is bad enough ischemia may already show up in 12 lead. Perhaps the original complaint was not cardiac in nature but it could be progressing to a point that it will be.
As to cost. Really not that much, instead of the 3 or 4 for your 3 lead you use 10 electrodes so even if a dollar a piece wow it added 6 or 7 dollars to the cost of care. Not that much in the long run and especially if you catch something and keep patient from crashing. A complete exam is the best exam.