Making one of something where the cost is no object is almost always possible. Making millions at a commercially-viable cost is much more challenging.
The entire Apollo program had a budget of $165.5 billion (in 2021 dollars), over a 10 year program. $16.5 billion per year. It's a big number, but it's absolutely dwarfed by things like a $600bn military.
Apollo was actually pretty close to the same GDP share (2.5% of GDP annually) as the modern defense budget (3.1% of GDP).
Inflation-adjusted numbers ignore that we have more people and more value produced per capita now than in the 1960s.
I don't have the numbers though.
Yes, the spending on the Apollo program is pretty close (as share of GDP) to the current military budget, not to the contemporary (1960s) military budget, which ranged from a 7.6-9.4% of GDP.
When you're sending a probe to Mars, the trial runs are very expensive. They spend a lot of time making sure that the mission will be successful. I'm skeptical that anywhere near the same level of care is going into the private missions, but I the reason is cost, not that they can't bootstrap themselves up with Earth-environment experimentation.
Yes, I'm aware at least one of the Mars probe missions totally failed. I don't think that detracts from the overall point. They weren't screwing up a bunch of missions before they got one right.