Well, if I were you (and I'm no genius model builder) I'd start with a basic wire frame and then put masking tape over it until you've got a basic shape you want. Then I'd paper mache it (nothing fancy...just take some shredded-up newspaper and dip it in starch, just like in grade school...), apply it to your masked tape Goji, and then let it dry. Do this until you've got the right shape. Then, if you have an airbrush, you can paint it as you wish. If not, basic acrylic paint and a paintbrush will do in a pinch.
It's nothing fancy (If you are talking an actual MODEL with molds and everything, good luck and godspeed
), but it'll cost you probably a resounding total of $5-$10, take only a few hours, and can be done with little or no blood, sweat, tears, and most importantly, experience.