Are you strictly a 2-wheel recumbent guy? I picked up a Catrike Trail last spring and had a blast riding it all year. I can see how it could get expensive if you get more than one, but at least for now it's a pretty inexpensive hobby for me.
Photography is my most expensive hobby at the moment. Lenses and lighting add up quickly.
My other expensive hobby is RC car racing. I always feel like I have to put a qualifier on this one when I mention it to people. It's probably not what you're thinking. These little cars are fast and infinitely adjustable. You name it, you can adjust it. Camber, Toe, Caster, Tires, Ride-Height, Motors, Batteries, Weight Distribution, Spring Rates, Damping, Roll-Center, Droop, Gearing and the list goes on. Below is a youtube video from the world championships a few years ago.