From the website: 'L$10 are taken for every uploaded image [into SL]. A 3D model from Archipelis Designer will be converted into images to get scuplty prims definition (one image per shape and one image per texture of a shape). Thus L$100 to L$200 is required for one model (hopefully, it is a small amount of real dollars).' Here, it's my understanding that they're talking about how many shapes you use to create your model. So, depending on the complexity of your model, it could very well cost a bit more.
Now, not having used Archipelis Designer, I can't verify how difficult or easy it is to create a model. At $55, however, it's a fairly inexpensive modeling program, and the Exporter itself goes for $5, so if you think you might have a future in content creation in SL, this might be a great investment to make.