Digital BW, The Print

I bought a set of the MIS quad inks for an old, large-format Epson 
(Stylus Pro XL) but am not able to make use of any of the suggested 
photoshop 'workflows' -- since I don't have Photoshop (and don't 
intend to shell out $500 or whatever to print B&W on this printer).  
Does anyone know is there any cost-effective image editor out there 
that can use Photoshop curve files?