If you've already shown that you are responsible when it comes to pet care, you could take that route. Let them know that you realize a bearded dragon is too expensive for one person to give to you as a gift, but if people didn't mind clubbing together, it is something that you really want. It could provide you with pleasure for years to come, as opposed to short-term gifts. Also, the fact that you would be able to tell each person what they had contributed to buying, e.g., the lights or vivarium, would help them feel reassured about their contribution, and they can feel as though they had 'bought' something of value to you.