In our town (Dundee, IL) is a Cassidy Tire shop that does wheel alignments primarily for 18 wheelers. Check your area for such a shop. The alignment is done with wireless clamp-on alignment sensors that communicate with a computer on a stand. There is no rack or other apparatus that is size-restrictive. They charged me $150.
Here is our rig being aligned. There is no limitation with the size of the rig.
Here is one side offset bushings that were installed 14 years ago.
Here are the alignment specs for our 2007 E350 chassis.
This is the best they could do without making a science project out of it and charge me 2x to 3x the cost with no guarantee it would be perfect.
HINT: If you have a Safe-T-Plus or other aftermarket steering stabilizer installed, make sure they loosen it's clamp to the steering linkage before they start the alignment.