Get a grip on how well your website does its selling. Just look at your stats and do a little mathematics. Affiliate.
How much a domain visitor is worth to you. If you get one thousand visitors a week and ten sales in that same week, then your visitor to sales proportion is 100-1.
However, few event planners have the posh of an unlimited budget. Your head honcho may like to drink poo on a lager budget. You can do it yourself or hire a company to cover behind.