Allow for MSRP to change over time

[driscoll42]

Is your feature request related to a problem? Please describe.
MSRP prices can change over time for various reasons, and currently the code cannot handle this. It assumes the MSRP is constant over time. This is an issue for instance when the tariffs went into affect on graphics cards on 1/1/21 and the code calculates profits as if it were the old price.

Describe the solution you'd like
The user should be able to set the MSRP to change on a certain date and the code will use the new price in future calculations.