When I'm building models I use a bunch of different paints. I usually airbrush my own color blend of testors model master acrylic airbrush paint, which isn't super cheap. But a lot of the smaller sections of the models you have (I've built the voyager and the reliant, but never seen the B5 kit so maybe this won't apply) can be nicely painted with super cheap cheap craft acrylics. Go to a craft store and find them. Here in the pacific northwest, I usually wind up with ceramcoat acrylic. A bottle will last me literally years. It's kinda thick coming out of the bottle, but it thins with water. Experiment and find the best mixture for your tastes. I notice you're in the UK, so I don't know what's available by it's brand name. But I've used the cheap stuff on Games Workshop models along side their own brand of Citadel Paints and the difference is marginal. With practice, you can get just as good.
Also, brush up a bit on color theory and by a limited range of paint colors. I almost never use a color straight from the bottle. A little tweak here and there and you can blend just about any color on your own. For me, I usually a keep a good black, white, red, blue, green, and yellow. I'll usually keep a couple browns on hand too just to make those more neutral shades a little quicker to get to. I will grant that Citadel makes some excellent metallic paint, so if you want metallic, I do recommend them and they are available in the UK for sure, but they are pricey. I bet you could get through the whole project with a dozen or so bottles of cheap paint and handful of classier ones. If you're not afraid to mix them that is. I highly recommend you experiment with it and see what you can do.
--Alex
