HA, ,most of the fab shops I have seen around here don't exactly have the tooling or experience to charge more than 40 bucks an hour. Before paying for work ask to see the shop and look at how organized it is. If they have effective quality tooling they can get the job done quicker, only if they know how to operate their equipment.
Here are some ideas for fabricator/4x4 mechanic work
Little experienced side jobber guy with limited tools $35-55hr
Guy with a shop, company name, some tools, not much experience $65-70
Actual Fabricator/mechanic with 10-15 yrs experience, certified AWS welder, MIG/TIG, machine work in house, Autocadd/3D/G-Coding, Prototyping/Jig work, Stocked shop with hardware and Steel $95-120 Hour
Hope it helps, I use to be a structural steel fabricator years ago after college, did the estimating thing, Detailing, QA for AWS/CWI.