Bad Injectors

Hi everyone,
I have owner my 2006 f250 6.0L for roughly 3 years and have poured much more money into it that I would like to admit. That being said Im invested in the truck and need it for work as Im a masonry contractor. Its been out for two weeks now as I waited for a local diesel mechanic to take a look. The news came in today, three failing injectors (1,3,8) and I knew this was worst case scenario. On my initial discussions he said if they were all on same side that he would suggest replacing all four which wouldve been around $2000. Since they are on both side I knew it wasnt ideal and on top of that he suggested replacing glow plugs and a couple of pigtails. His estimate was now $6000, which seems a bit steep considering the glow plugs are something that I would and could do. Just looking for advice as to what I should be looking at for replacing all 8 injectors, I was thinking $4000 would be the absolute max. I recently replaced tranny and I have a couple of other things I would need to do as well and not sure its worth it chasing my tail with this truck. Any and all input is appreciated. Thanks in advance. And for the record, I know a very little when it concerns these trucks, just trying to figure out where this price got so high.