It would possibly help if you learn to breathe from your diaphragm rather than from your upper chest. It might help you get a more resonant sound, although it wouldn't deepen the pitch. I've always played woodwind instruments, so we learn that breathing technique.
Try putting one hand just above your belly button and feel your chest moving in and out. That big band of muscle you can feel pushing is your diaphragm (apologies if you know this already!). Now, stand in front of a mirror, pretty close up. Breathe in, and feel your chest expanding. Breathe out slowly, and try to mist up the mirror with your breath. Once you've learned to control your diaphragm, you can mist the mirror up evenly instead of in a few bursts. You can also try holding a piece of paper against a wall and keeping it there with your breath.
But also, don't feel you have to worry about sounding nasal. Depending on where you're from, some accents are nasal anyway, and not all guys have big rich voices.