Greenhouses don't have to be terribly expensive, but they certainly can
be depending on the model and style.

Question: does this fireplace take up the entire wall? Might you leave
the fireplace and chimney, but have the walls knocked out (granite or
whatever) and put in some windows. If you combined this with the
greenhouse idea, you would end up with a semi-freestanding fireplace,
which can be very nice.

-Kevin