Couple of thoughts:

1) The main thing is not to be deceptive with your prospects about how you're going to use their information. If you survey them, and they provide contact information to you during the survey, and then you start hitting them with promotional materials--without asking for their permission--they will find this deceptive. This is not the way to build trust. Instead, as you collect their information, tell them exactly what you are going to do with it. If you want to wait until the end, and ask them then, that's fine--but I would ASK them for permission, i.e., "Thanks. As I said, I will be publicizing this information in aggregate, so your input is anonymous. However, now that I understand your needs, I may be sending you things from time to time that you might find useful. [It's always a good idea to tell them how OFTEN you'll be sending them--like, every couple of months or something. Otherwise they will be worried that you will overwhelm them.] Would that be OK with you? How would you prefer to be contacted? If they say NO, then just respect that and don't add them to your contact list.

2) I don't think offering a prize is a good idea. After all, you're contacting them at work, they're in a work mood, and you're asking work-related questions. "Prizes" don't fit well into this scenario. Also some companies have policies about accepting gifts from vendors, in whatever form. I have found that people would be interested in the results, so you can offer to send them the results of the survey--after all, you're asking them about their issues, and asking others in their field about the same issues. Most of us like to know what our peers are thinking. This could be the first thing you send them, and it would be asked for and useful--which is good.

I would also wonder what questions you're asking them. It's better to ask open-ended questions than to ask specific questions, which are often from "your" head rather than "their" head, and so you can miss important issues that could drive your sales.