It is helpful for Renters to have "SOME IDEA" of what the price of Siesta Key Rentals will be, and then consider shopping for Rental Units in their budget. It is understandable that folks who have never rented on Siesta Key might have no idea what a rental may cost them.
Here is a VERY GENERAL OVERVIEW of Siesta Key Pricing in Peak Season (Feb-March-April) for a 2 bedroom / 2 bath unit.
These are "ballpark" averages, yes it is possible you can beat these prices, but it is a waste of time to seek a direct beachfront in season and think they are available for $3,000 per month, that just isn't realistic. So the message is to have realistic expectations for your budget.
Yes some discounts are available (at some places) for renters who book multiple monhs - BUT the truth is do not expect more than 5% to 10%. (So for example a unit that rents for $8,500 per month MAY be available for 3 months at a 10% discount (List Price: $25,500 - discounted price: $22,950). But often owners would rather rent the individual months at full price than give up (for example) $2,500 for the season. But all owners are different, so it doesn't hurt to ask.