How much would it cost to have a new computer put into a jeep chorokee? or to have one repaired?

the last cylinder in my 91 jeep cherokee 4.0 is not working and i have traced this to beint that that particular injector is not recieving power. i believe thi injector to be good but there is no power going to it so i cannot know for sure. the positive and negative wires had came disconected from the harness and they touched together which i believe would have grounded them out and that would cause the problem. how in other electrical systems this would have simply blown a fuse. well i donnt believe this system has a fuse in place. so does this mean i need a whole new computer? or could this be repaired and what might it cost me? i hope someone can help thanks for any help i can get.