Do you mean that they are too big to iron because they are too big for the ironing board?
I have been known to clear a space, throw down a duvet cover or sheet (pull it tight to take out the big creases) and use that as an ironing space. I then steam iron the curtains on the reverse side. I used to work in a curtain designer place years ago with huge great cloth covered work benches so you could iron great lengths at a time.
If you don't have a steam iron then use one of those mist spray things...or, buying a stream iron would be cheaper than the dry cleaners.
if you take them to a dry cleaners, they will most likely price them by weight. If it is a press only i think they half the cost of the full cleaning price. Call the cleaners and ask them for a guide price then weigh them on scales, should give you a rough idea.