6k? Are you trenching through granite? Even in hard Texas caliche, if you wanted to go 42", you could get that done in a day with a 6' x 48" trencher. If you are in dirt, figure on a half day. I trenched 100', 3' deep in less than hour with my Bobcat high flow trencher. I trenched over a 1/4 mile, 5' deep exactly, through dirt, caliche, and mixed rock with the same trencher and it only took about 16 hours and part of that was backfill time. Even at that depth in pretty hard ground and including backfill, if my math is right, 600' should take just over 7 hours. If it's all dirt, it should be like cutting through cake.
Maybe I should move to CT and start a trenching service! For about 6k, someone could get me to mulch for almost 5 days if it's local and not too rocky. I charge more for rock (same with trenching) but for a 6k job, I'd have 1/3 of my trencher paid for and it would still take only a day in moderately hard ground. Wow.