You can add a sidecar to your bike way cheaper than putting a trike kit on it. Check out Hannigan motorsports.
www.hannigantrikes.com , they do trikes, but also sell and install a wide selection of sidecars, from small, lightweight ones to others that will easily carry 2 people. There is a learning curve to riding with a sidecar though, it is a lot different than being on 2 wheels, or a trike.
My wife and I both have Hannigan sidecars on our bikes and are very happy with them. We did a four month, 15,000 mile ride on them last year, and had a blast.
Besides, sidecars are way cooler than trikes. Everywhere we go people come over to check out our rides.
And no, I don't work for Hannigan.