Although you asked the Group for advice, it seems that you may have already eliminated all three of the choices based on your budget (280), lack of storage space (240 shell) , and current mechanical skills (240 shell & rusting 260), Keep in mind that these aren't the last three Zs on the planet. As others mentioned, expand your search area. Find a local club or ask around at local mechanic shops to find unadvertised cars. Most of us didn't have the pleasure of buying a Z new off the showroom floor. So, for most, it became a hunting adventure. Take your time, the right car is out there.
You mentioned that you have three parts cars 800 miles away. Condition? What can you salvage if needed for the Z you eventually find? Enjoy the search and count on this Group to help.
Dennis