Please follow this:
go to https://eternity.obsidian.net/backer/index and log in if you aren't already
Your first screen should look something like this. Please note it is shown as (1) Pledges on the Scale at the top of the screen
Press Select Reward down the bottom right and continue on to the second screen (2) Pledges as shown on the scale up top
Unless you want to upgrade your pledge, which you don't, click the button for the $140 pledge and then click Continue to next step
You will now be on the (3) Addons screen as shown on the scale up top. You stated you don't want addons so click Continue to next step at the bottom
On the next screen, click Checkout, enter your relevant details and the rest should be obvious. If not, ask again here and I'll do my best to help
I hope this helps end your frustration