For info on the cost of the LM project, I refer you to this source:

"As expected, the proposal price increased dramatically by the time we finished the negotiations and included all the testing and support items in the contract. The original lunar module proposal was priced at $387 million. After negotiations, the price climbed to approximately $1 billion. By the early 1970s, toward the end of the program, the total cost was closer to $2 billion, approximately a tenth of the total Apollo program cost."

While this isn't completely accurate, $2 billion in 1970 dollars is equavilant to $9.13 billion today. That $50 million per-unit LM price most definitely did not include R&D. Oh, and $50 million in 1969 dollars is equal to $241.28 million today. Inflation calculators are useful things when comparing prices from different eras.

Yes, computer equipment has improved dramatically since the 1960s. However, most computer equipment isn't suitable for space use due to the higher background radiation levels. Radiation effects, especially gamma and cosmic rays, causes random bit errors inside of densely packed computer chips. These errors are known as "Single Event Upsets". The chips have to be radiation hardened and the computer's have to be able to handle SEUs without crashing. Not many off-the-shelf computers are up to the job.

You need to so some research on what aerospace projects cost. It costs millions to get a private plane certified for production, and it's only that low if the plane is no more complicated than a garden variety Cessna (fixed gear, metal construction, etc.)

Developing a lunar lander, even one built from off-the-shelf parts, will require the full time effort of dozens of engineers and machinists even if you used the Skunk Works management model. People with that level of skills don't come cheap and you'd need them for at least 2-3 years to build the lander. You'd also need millions of dollars in machining equipment, facilities, etc. Just writing the software for the lander would likely cost upwards of $100 million (good geeks don't come cheap, either) when you count all of the testing necessary for such critical code. Those off-the-shelf components aren't cheap, either.

I support returning to the moon. I even wrote about my concepts for a lunar lander design just last week. However, I also know that building such a design, especially if it's intended to be reusable like I want, will cost at least a billion in R&D, test, fabrication, etc. After the first one is built, building follow-on vehicles would be a lot less expensive.