Formula to return value based on two criteria

I have a seasonal business and I am trying to create a spreadsheet that pulls a historical average capacity number based on two criteria, week of the year and day of the week. I can get that working both with vlookup and sumifs formulas. There is a third variable involved and that is what I am calling special days (christmas, new years, etc.). I have tried different variants of index and match statements, nesting if statements with sumifs but I am not having any luck.

My desired outcome is this:
- Reference column A and B on the Capacity Data tab
- If column H on the Daily Budget Day over Day tab matches column B on the Capacity Data tab, return the value in column C from the Capacity Data tab in column I on the Daily Budget Day over Day tab
- If column H on the Daily Budget Day over Day tab is empty, match column B on the Daily Budget Day over Day tab to column A on the Capacity Data tab and match column C on the Daily Budget Day over Day tab to column B on the Capacity Data tab, return the associated value from column C on the Capacity Data tab in column I on the Daily Budget Day over Day tab
Snowsports Instructors - 2015-2016.xlsx
Thanks for your help!

Thanks skywriter, that did the trick!