When I did the sales run, I promised I'd initial and sell off the beta cart, which I made before the final run to take up to a convention in San Jose and show off. Well, turns out EBay doesn't like betas, so it was suggested I try it here!
What I've got here is the beta cartridge for the TI-99/4A, the original proof box, and I threw in the postcard and posters that all the final releases got as well. Pictures of the actual unit are below. There's only one and will only ever be one.