Turbo Tax is saying I have to upgrade because I need (Schedule D) which requires Form 1040. Can I continue to file with free version and mail in the schedule d?

I don't understand what you mean by "Schedule D, which requires Form 1040." All tax returns require Form 1040. That's the basic, primary tax return form that everyone must file.

No, you can't file Schedule D separately. Schedule D has to be filed together with Form 1040. But besides that, if you somehow eliminated the Schedule D, your Form 1040 would be wrong. They have to be prepared and filed together.

Well, TT charges $90 fed + state for schedule D and some filers  have very small gains from trades - $100-200 so it's rather preposterous to pay so much for schedule D plus the tax on these trades. Therefore I and maybe the poster above wonder if one can file taxes for free w/o schedule D via TT and them amend them at a later time by mailing them with a payment which will be very small $20-40 therefore saving money.