“Wrong...... minus appropriations there can be no contracts.”
Wrong.
You can negotiate and establish contracts, you just can’t commit funds (order anything) without appropriations (Anti-Deficiency Act).
Contracts can (and many do) exist separate of funding - they are mainstays of Government procurement.
Contingency contracts are standing vehicles pre-negotiotiated and ready to accept funding in case of disasters, emergencies or military need.
Indefinite Delivery/Indefinite Quantity (IDIQ), and Blanket Purchase Agreements are common Government contract types, where one (expert) Agency establishes a standing contract, and other Government customers can come with their own appropriated funds to buy goods or services - almost anything you could imagine.
The US Army Corps of Engineers manages several such contracts for construction related services, such as the Multiple Award Task Order Contract (MATOC) for Horizontal Construction Services in support of the SW Border Patrol Sectors & SWD Fort Worth District (an IDIQ contract vehicle).
The point is that it takes a significant lead time to initially establish such a contract, but once it is in place, you can quickly commit funds with it.
Construction projects require a design phase, which must be completed before construction can start. FOIA requests are now coming out that show that the design phase has also been underway for some segments, like this one for three milles of the Rio Grande Valley Sector near Alamo, Texas (Eastern edge of McAllen): https://www.documentcloud.org/documents/4199097-Border-Barrier-System-RGV-01-DRAFT-PMP-29Jun17.html
Bottom Line: A lot of long lead time work required for a major construction project has been underway this year, to support border wall construction - administrative, legal, survey and design.
Ok, Ok...... you are correct.
However in the absence of the money the contract will never be carried out to completion.
I see no chance of successful congressional action to provide the money