Unless you're building an ultra lightweight trailer, I think you're right about cost and weight. $10 and 20lbs that you can drop in vs. more $$, and you have to build whatever surface you use.
I'm fond of plywood with a laminated surface that gets a hardwood edge. Inexpensive (NOT as cheap as your CT, though), strong, and you don't need as much support for it. If you have a router with a flush cutting bit, the laminating process isn't that hard either. You can get smaller pieces of the laminate fairly cheaply as well.
Since you will not save that much weight with other options, it makes sense to just use the laminated counter top you have.
Michael