People don't have great ideas on what they'd do with new monies that would come a 10xManhattan size project. Tesla, VW, Toyota, Dept of Energy, DARPA, NSF, Energy Companies, Industrial Conglomerates like GE, Panasonic, etc. all work on battery research. (& many more)
The actual Manhattan project could spend the funds by building reactors with desirable end-products (uranium etc.) and building a lot of centrifuges to refine it further - along with engineering teams to design, build, and operate these things, various bomb and delivery mechanisms etc. It was the very beginnings of nuclear science, so there were many fundamental ideas to be discovered and tested out - it meant sense to spend a lot of money to travel and explore this newly discovered branch of the tree of knowledge.
The actual Manhattan project could spend the funds by building reactors with desirable end-products (uranium etc.) and building a lot of centrifuges to refine it further - along with engineering teams to design, build, and operate these things, various bomb and delivery mechanisms etc. It was the very beginnings of nuclear science, so there were many fundamental ideas to be discovered and tested out - it meant sense to spend a lot of money to travel and explore this newly discovered branch of the tree of knowledge.