The employer should definitely be paying for an ergonomic setup. They are liable for any injuries that occur on the job as the direct result of a poor setup. I suffered a wrist injury at work because of just that reason, and the employer had to pay for workman's compensation and make accommodations for me at work with my setup. Don't let this escalate to an injury, and it very likely could -- not to scare you, but this is important and necessary. Do you have a Human Resources department you can approach about it?