What can't I deduct my $35 in mileage expenses related to my $437 in side job income without paying $70 for a TurboTax upgrade?

If you have expenses in your self-employment work like your mileage, you'll need to use TurboTax Self-Employed. Each version of TurboTax is designed to handle different tax situations and their associated forms. 

The fact that you need to self employment forms to file requires the upgrade.  TT isn't sophisticated enough to allocate the fees based on the amounts going on the form.

TurboTax also has another free product called the Free File Edition (not to be confused with the regular Free Edition).  It has free Federal preparation and free State preparation. There is no efiling fee. It is not available after October 15

The Free file Edition can handle a 1099-MISC.

The Free file Edition is more fully-featured than the regular Free Edition.  The Free File Edition can prepare Schedule A, C, D, E, and F that the Free Edition cannot. 

To qualify for free 2020 federal and state tax returns through the IRS Free File Program delivered by TurboTax, you just need to meet one of these requirements:

• Your 2020 household AGI is $39,000 or less;
• You qualify for the Earned Income Tax Credit (EITC); or
• In 2020, you served as active duty military (including Reservists and National Guard) with a maximum AGI of $72,000, and you have a military-issued W-2.

The FREE FILE Edition is located at:
https://turbotax.intuit.com/taxfreedom

How to switch and start over in Free file Edition
https://ttlc.intuit.com/questions/2026912-how-do-i-switch-to-turbotax-freedom-edition