The Trinity test was of a plutonium device. There were no doubts about the U-235 bomb. But there were questions about the plutonium approach.
The “gun bomb” was fabulously expensive and time consuming to make. I’d even hate to venture a guess as to how much it would cost to build one in today’s dollars and electricity costs.
At one time, Oak Ridge consumed 1/7th of all of the electricity generated in the US!