The ICSC citywide convention moves in that weekend (Intl Council of Shopping Centers) - the LVCVA's website says it has 30,000 attendees. If you are trying to stay at one of the properties where they have their events, this may be why you are finding higher rates.
Did you try VRBO.com? We're going May 15-19 (our Victoria Day long weekend) with extended family. We got 3 jr. suites at the MGM Signature for $149 per night (includes housekeeping fee). We did book about 3 months ago to get this rate. Hopefully, you can find something directly from owner on that website.
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