Convince those sponsors
You now have an elaborate plan and budget. Now you are in a good position to approach the sponsors you identified. Tell them about the event, the objectives, why they would be the ideal sponsor, and what you need from them.
There is no room for error. Things like your communication style, approach, reliability, and punctuality count. Make sure you are clear about what you need from them. Be ready to justify your request.
There is always the chance that the prospective sponsor will turn you down, forcing you to approach others. In such instances, just dust yourself and move on to your next prospect.
Tip: To learn more about getting sponsors for an event, read this detailed guide.