Restoration and maintenance personnel are some of the most important volunteers in the CAF (the most important in my opinion). The only financial requirement of which I am aware is simply being a dues-paying member of the organization. There are multiple levels of aircraft sponsorship (see
https://commemorativeairforce.org/pages/Become-an-Aircraft-Sponsor). In ascending order they are Supporting, Restoration and Aircraft/Pilot Sponsor. Each give the sponsor the official "Sponsor" designation. The Restoration Sponsor program is mainly a program for folks who want to generously support a specific aircraft and be classified as an official Sponsor, but may not rise to the donation level of an Aircraft/Pilot Sponsor, or are working on becoming an Aircraft/Pilot Sponsor (PIC). In terms of being a maintenance personnel or non-FAA required crew (PIC, SIC, Flight Engineer, etc.), it is not required to be an official Aircraft Sponsor. That's what makes the CAF so great, for your annual dues/life membership, you have access to amazing pieces of history all over the country and abroad, including opportunities to wrench on, crew, or otherwise support the aircraft, the wonderful members, and the admirable/necessary mission to Educate, Inspire, and Honor.