Scott, your idea sounds a lot like an i-joist
They can be had for £17 for an 11’6″ beam in the UK. That is for what amounts to a 2.5″ x 9″ beam, with bigger sizes available. Supposedly as strong as the equivalent timber dimensions, but obviously a fraction of the weight.
Also, they’re on eBay over here, but couldn’t find them in US eBay. Different name?