Best Practices for a linked table in Power Query - create on the fly?

Hi, I'm new to Power BI. I have 2 data files loaded as tables into Power Query, one is a listing of cars, the 2nd one is a listing of sales projections with a low, medium, and high sales prices for each specific car based on condition, type, etc. I have a join on the ID # between the 2 tables. However, what I really need is a 3rd table that pulls several columns from the first table (car listings table - i.e., ID #, make, model, year) and does some calculations on payments for those cars based on the sale price (sales projections)--i.e, if I select a 2005 Nissan Maxima from table 1, and then the "Medium" sale projection, I need to see what the estimated monthly payments would be. I can handle the calculation, I'm just wondering about how to create a new table to store the data from these tables. Or is this the right way to go about this? Ultimately, this will be displayed in Power BI visualizations. 

Here's a sample of data

AUTOS (table)

AUTOSID |  Year  | Make   |   Model   |  Color   

1                 2006   Honda    Civic         White      

2                 2009   Kia          Optima     Red     

SALES PRICES  (AUTOSID is the link between the 2 tables)

SALESID  |  AUTOSID  |   Type  |   Low  |   Mid  |  High

1                  1                  2 DR    2500     4500    5000

2                  1                  4 DR    3000    3700     6000

3                  2                  2 DR     4000     4200    4800

4                  2                  4 DR     4500     5000    6500

Now, the table I don't have yet should look something like this...

PAYMENTS

PAYMENTID   |    AUTOSID   |   SALESID   |   Lease Term  (Months)  |  Monthly (Calc)

1                         1                     1                     30                                 120

2                         1                     2                     30                                 124

3                         2                     1                     30                                 124

So....

1) Do I create a "shell" spreadsheet CSV with the columns listed in the PAYMENTS table above or do I create the table on the fly in Power Query?

2) Is there a better way to do this? I'm still new, so I don't know if I should be creating the data on the fly here, or do it somewhere else and then just setup the column formulas and linking in Power Query for BI visualizations.