You didn't say what resort you were looking at, but when I checked the Caribbean Beach resort and Pop Century prices for Monday, Memorial Day, it was the week day rate, the same daily price as it was for Sunday through Thursday. It wasn't higher on that date.
Here is how to see the daily rates.
1. go to the website:
https://disneyworld.disney.go.com/
2. put in your dates, # of guests
3. hit "find rooms"
You'll see a list of resorts
4. In order to check the daily prices, click on the arrow to the right of the ave/night prices. Then you'll get a list of room types.
5. Click on the words "view price per night" (it is right below the average price) and you will see the rates for each night of your stay.
The secret is to click on that arrow to get to the page that lets you check the daily rate.