Yeah, the 747 used to cost 21 million it now costs nearly 400 million to build. But that's my point. What makes your think the cost of airplanes has gone up so much but the cost of reaching the moon only costs 3 airliners? If moon landings are so cheap, why hasn't anyone done it since the Apollo missions?
Keep in mind there is multiple ways to look at launch costs and it can get very confusing. It is hard to even track down firm numbers sometimes on Space Shuttle costs.
#1- You have to consider facility costs. NASA has a large incremental fixed cost for all the facilities etc. to support it's operations. This can have a variable impact on your per launch cost. Example if your fixed facility costs are $2 Billion a year and you have 4 launches, well that would mean $500 Million added to each launch. However if you have 8 launches that means $250 Million added to each launch. Looking back it makes it hard to pin down exact numbers. You can see this affect during the Space Shuttle stand-downs and NASA still spent Billion's on the Space Shuttle during years with no launches because all those assets and people still needed to be supported. You cannot just lay off your check-out crew and expect you can hire a new crew in 18-months.
#2- You then have the actual operations cost for launches, fuel, transportation of the launch vehicle etc, checkout of cargo going up. Those costs can represent easily 30%+ of a launch cost.
#3- You then have the actual vehicle cost. For the Saturn-V this is your actual cost of production. However which number do you use the actual incremental cost or do you factor in the R&D cost? Then that means the more launches you have the more ways your D&D costs can be split.
#4- If you are launching the Saturn-V, what are you launching? Well if you are going to the Moon you have the Command Module, Service Module and Lunar Module. All this hardware costs money and should be added to the mission cost.
Sometimes the actual easiest number is to take the total program cost which was about $130 Billion (It is even hard tracking down this figure) and then divide by number of flights. However which flights do you include? Do you include the un-manned and manned flights that didn't land on the lunar surface? If you just take the total program and divide by six you get a total cost of about 21.6 Billion per lunar landing.
Now to your question on why the lunar landings haven't been repeated.
Hardware, Hardware, Hardware.
The tricky thing about producing Aerospace hardware like Launch Vehicles, spacecraft, airplanes etc. Is that once a production line is shutdown it is very hard to start that production line back-up again. Congress and the Nixon Administration in it's infinite wisdom decided to shutdown the Saturn-V and later all the Apollo hardware production lines starting in 1969. That means we lost or ability to build the Saturn-V, Apollo-CSM and Apollo-LM. So in order to go back to the Moon you would need to develop new hardware which is very expensive and then build it and then support the mission costs. Right now NASA has spent close to $20 Billion to just develop the SLS and Orion which would replace the Saturn-V and Apollo-CSM for a lunar landing. You would still need to develop the lunar lander. So to just develop the hardware for a lunar landing you are probably looking at close $30+ Billion. That is before actual production and operations cost.
So does that answer your question about why the lunar landings haven't been repeated?