There are estimating references available both on line [for a price] and likely at a local library in a larger city.  R.S. Means is a standard text or set of texts that cover essentially every industry and aspect of construction.  They take into account the basics ie: materials, time, consumables but go further and evaluate regional location and comparative labor costs, transportation and other factors.  It is not always useful if you are bidding the job competitively but they are worth it for change orders to demonstrate "historical pricing" and the justification for costs.  Most state DOT agencies recognize the schedule of values Means expresses and won't/can't argue against it.  You might even try getting through on the phone to someone in their office, explain your precise fabrication and tye may be able to reference a price for you.  It may surprise you what the real cost of manufacturing/fabrication really are.  The first time I looked through one of their pipe fabrication cost tables and saw a 6" sched. 40 weld factored at 4 hours I almost passed out, but when you figure all the actual costs and labor that go into getting that done- transports, material handling, fitting, welding, inspection, loading out, delivery, paperwork it looks less improbable.  If nothing else it might be a starting point for you.  I would be talking to management above your pay grade to start learning more about what the company has charged in the past, what kind of profit margins they try to maintain, what paperwork do they save from earlier bids you could learn from.  You may be in a position to expand your understanding of this industry in a manner few get the chance to do and you might be able to do it without having to eat any more welding smoke for the next few decades which might not be the worse thing either.  Managerial skills have their benefits at a certain point in your career and you're being handed a chance to obtain them.  Good Luck