If you want to identify genes associated with a certain phenotype in a case-control setup you should not limit yourself to a set of predefined genes. Just extract the RNA from multiple biological replicates of each case/control and run a RNA-seq analysis genome wide.
Price is always relative to what your budget is and how many samples you are looking to analyse. As far as I'm concerned it costs around 180-200$ per sample byt this may differ from country to country.