EK Rip also has the ink estimate calculator, any good rip should have this feature..Here is an easy way to calculate ink cost on any design.
Download a copy of Multi Rip. It's fully functional except it prints a watermark if you use it to print t-shirts.
You can enter the cost you pay or expect to pay for inks and then pick a design like you are going to print it and it will calculate the cost to print the t-shirt.
the cmyk prints are reasonable, its the white ink printing cost that is the biggest issue.. some if not most decent size prints 12x10 or so range in the 2 to 3 dollar area per print (just the white ink) add pretreat cost on top of that plus shirt cost/ labor/waste ink and it is not very appealling for the low volume printer and certainly not profittable... on top of this if you have one issue with the printer like a clogged head you will be in the hole on profits and down with the machine...