We have an 1890s Victorian, fabulous HUGE windows, which work great for
natural cooling, but we're installing central a/c and heat. Some panes
are broken and have to be replaced anyway, but what can we replace them
with, without replacing the entire window (for $860/window!)?

What would be the most energy efficient, given the size - can't do
double pane because there's not enough space. We can re-work the
windows ourselves a bit to add an extra 1-2/16s of space to fit glass,
but would such glass be any more energy efficient than what's there?

We have 14 windows - most 8ft x 3 ft (one is 8 ft x 6ft, and 2 are
smaller). Eventually we'd like to make all more energy efficient, but
for now, will just replace the broken ones.

Thoughts?