The short answer is no. All LL$ prizes are paid by the slegghunt account, and there is no requirement to add any prize if you don't want to. Many sponsors choose not to add any freebie prizes at all, particulartily if they place a lot of eggs. Some sponsors hide the prize in the most difficult egg, some pick a day that correlate with a scheduled event to give out prizes. It's really up to you.

 In 2008 Lorimae Undercroft commented on no prize eggs vs. eggs filled with freebies everyone already has. Her opinion that no prize is preferrable to endless repeat freebies has been echoed by other participants and players of The Great Grid-wide Goldrus. You can read her take on the matter here: SleggHunt Observation Regarding Prizes.