How much did Apollo space program cost?
According to Wikipedia, the entire Apollo program cost $25.4 billion (as reported to Congress in 1973), which is roughly equivalent to $150 billion today (adjusted to 2018 dollars).
Some other estimates can be found on Apollo program - Wikipedia .
One could say that a lot of the Gemini program was aimed at the same goal and could be included. On the other hand, one of the Saturn V rockets built for the Apollo program was used to launch the Skylab space station, and two Saturn V rockets were never flown.
How much did a single mission cost?
You could divide the total cost by 6, for the six missions that landed on the Moon (Apollo 11, 12, 14, 15, 16, 17) and get $25 billion (2018 dollars) per mission. Had they chosen to continue the program and send more missions, the cost of each additional mission would be much lower than that. Nevertheless, the costs were quite high and they decided to put the resources towards other goals.
Estimating the cost for a single mission is tricky because initially, the Apollo program was managed as a whole. Some estimates were done when they were deciding whether to continue the program. A Saturn V launch was estimated at $185 million ($1.2 billion in 2018 dollars). Note that that’s just to build and launch the rocket itself and does not include any payload costs. Another estimate ( SP-4221 The Space Shuttle Decision ) states $375 million ($2.6 billion in 2018 dollars) for a full moon landing mission.