It is very difficult if not impossible to price connection design on a $/lb or $/ton basis and several factors should be taken into account.
1) type of connection,(vert. bracing, moment connection, etc.) and are the connections straight forward, is there repition
2) is the job in a seismic zone (does AISC seismic provisions apply)
3) is the connection designer required to supply full calcs on all connections or can they do a sample and then just supply the detailer and EOR with connection summaries
4) Is shop drawing review part of the contract. I have seen shop drawing review costs exceed the actual connection design cost.
Many factors weigh into this, its not as easy as a price per pound. I have even been asked for a % of the detailing price which may be a little easier to come up with although still very, very ballpark and that could range from 20-30%
From what standpoint are you looking at this, the fabricator trying to come up with a price to add in for this or from the actual designer?
I agreed with Redfish. It's not straight forward as beams and column design where you can estimate the cost per pound. However, I use a rule of thumb for 30% for moment connections for multiplier for to the beam weight and 15% of cost to simple bracing. All include high strength nuts and bolts. It comes close to +/- 10% of cost estimate every time so far for me anyway. But that's not to say there are more scientific method since I've only done 12 or so steel detailing shop drawings.