OH NOES, PAYING FOR SOFTWARE, HOW TERRIBLE!
Cost: Fireworks $299
Cost saved due to productivity: infinite
Fireworks is always running on my computer as I use it heavily so it makes no difference to me, half the time I don't need to start it up. Even when I am starting it up cold it takes maybe 5 seconds. Whatcha gonna do with the *seconds* you saved by running a CLI program instead of an easier to use GUI app? Gee if I had all free time on my hands from the *seconds* I saved I just would not know what to do with myself!
And your CLI app might not need to export them. Big deal. Fireworks doesn't need to export the images either, if all you want to do is resize the images and save them over themselves it does that. But it's only 1 extra click to set the export step in the batch process and it optimises the images for the web as well as scaling them.
"Conversion, fastidious Goddess, loves blood better than brick, and feasts most subtly on the human will." -- Virginia Woolf, "Mrs. Dalloway"