Not trying to burn you, but I looked at your dB and I don't see how this will work.
Specific to your question, I suppose you could write a function (UDF) to get the pay rate. Or you could try using DLOOKUP() function. But both methods would be slow.
The some of the problems I saw were:
No PK field in any table, therefore no FK fields
No Employee (or worker) table,
No Contracts table,
Used reserved words as field names ("Name", "Type", "Start" "End)...... plus these names are not very descriptive. (Start of what?)
Work through these tutorials, actually create the dBs:
http://www.rogersaccesslibrary.com/forum/forum46.html
Then start creating your table structure using pencil and paper/ whiteboard/ sticky notes, before starting to create them in Access.
I don't have a whiteboard, so I use my window and a dry marker to design my table structure.
Only use letters, numbers and the underscore for object names; No spaces, punctuation or special characters in object names.
Good luck with your project.