That would be something like

1) if(this,then show this, otherwise show this) 
2) if(this, then show this) or if(this, then show this)

if(TransactionType="Sale", lookup("Uniform Store Inventory", "ID", Product,"Sale Value"), lookup("Uniform Store Inventory", "ID", Product,"Return Value"))

OR

if(TransactionType="Sale",lookup("Uniform Store Inventory", "ID", Product,"Return Value")) || if(lookup("Uniform Store Inventory", "ID", Product,"Return Value"))

When Use either of those formulas when I go to preview the the form to test it I get this error. 

It does not like when I use the TransactionType Named control. 

Sorry Gary, forgot to say that you need to update the named control to whatever you have.

by the way, you can have a calculated value with the lookup() function to ensure it pulls the information.

Couple of things, 

1, The lookup works fine to return the values for each product when I use:

lookup("Uniform Store Inventory", "ID", Product, "Sale Value")
lookup("Uniform Store Inventory", "ID", Product, "Return Value")

Individually in my formula, because they are on the same site. Its when I try to combine them I am having troubles

Uniform Store Inventory= The name of my list, Product is being pulled from the a different lookup that I am doing, populating the list of items in a drop down menu, I want to add the above combined formulas into my "Price" calculated control. 

2. That is what is strange TransactionType is the what my named control is called so I am not sure why it errors. 

This ended up being the final formula that I used to accomplish this. 

Formula Builder

@ Bim Bimi 

Thanks for getting me on the right track.