Hello Spook,
Sorry to hear that. The basic guidelines for retreatment are longer, stronger, add ribavirin – pick at least 2.
There is more on this here: http://fixhepc.com/forum/retreatment-corner.html
Although prices have fallen over the last year the longer/stronger bit means it will probably cost more for retreatment. You would be wise to wait about 6 months to get access to Sofosbuvir + Velpatasvir + Voxilaprevir which will be available this year (when the Vox arrives) and cheaper than anything of similar “kick ass” potency available now.