Si if there are many many 45's and 90's for 2" and above field bend works out to be cheaper due to labor/material? How and why as opposed to factory 90's . I
You're the estimater - take a lool at the numbers, and the costs of labor per unit. Pre-bent stuff from the wholesaler is expensive, and, it takes extra cutting and threading, to match up to whatever it is they sold you. Straight pipe is cheap pipe, but the world isn't built that way, you have to play with what is given. Ditch might not be straight, grades change, etc.
With a bender, and skilled craftsmen in the field, it will be a lot cheaper overall to set the men up with the equipment and bill appropriately. I can see 700 to 850 hours worth of pipework, before you figure out if it has to concrete encased, or if it has to be RGS (whatever the specs say). If you use alternative methods, do you have to cage the the road crossings? Hour adjustments for alternatives. Who trenches, backfills? Do you backfill to the top of the first lift? Scare tape? Me thinks you'll be busy with this animal for a bit. not to mention a shovel full of money.