I'm not entirely sure if I could find it again, but there's a website out there with open source models of sci-fi ships from all different brands. I think it's something like sci-fimeshes.com, but that doesn't sound quite right. I found it when I was looking for models to add into Celestia. I know when I ran across it that I found a whole downloadable set of models for BSG, including Vipers, Raptors, Battlestars, Baseships, and just about everything else. There's one rather poor model of the original BSG on the Celestia motherlode if you'd want it.
Otherwise, Blender is really pretty easy to use, once you get the hang of it, as is Google's Sketchup modeller. If you're willing to put in some of the more tedious work with it, you could put together some decent models in a few hours. I'd recommend playing with several of the tutorials in Blender unless you have some 3D modelling experience. It was really confusing for about the first hour I played with it, but it got a lot easier in a hurry. I've been working on a few models for a Firefly mod on and off. My computer isn't a fan of Blender's renderer, but I'm running an Acer (ugh,) that's really quite a pile, and I'm on Vista (double ugh,) Home Basic, (triple ugh.) If you're on anything more decent, Blender ought to work just fine for you. Other people around here might be able to help you with converting things from Sketchup to Blender better. I haven't had time to play with that much. I know it can be done, though. Sketchup is great for modelling, but I don't think it even has a renderer built in.
I'd offer to help you with this project, but I'm honestly overwhelmed with RealLife as it stands. Teaching junior high is consuming my soul and spitting it back out into glasses of scotch. If you were willing to wait until about late July for things, I might be able to give you a hand, but that's about it.