"You grossly overestimate today's materials vs 1960s. Not that different. The LEM WAS light. Very thin titanium and aluminum. The % of weight that's sturcure even then was miniscule. The weight was fuel & payload (crew). You still need far more mass than even 2 A5 launches could provide."

I would say you would need 3 A5 to get crew of two to the Moon and back. If all you wanted to do was land 2 crew safely to lunar surface, have them stay for a couple of days then return, then I would think the minimal and safe amount of boosters would be 3 [I don't know why you would want to do this though]. If you wanted to do something important/useful e.g. mission to lunar polar regions, to find water, extract some and process it into LH/LOX. Then it would take around 6 A5 type boosters. At a price tag of around 120 million per booster, you should be able to keep the entire cost of this entire mission for around 3 billion. And say the entire program length was 3 years it would cost about 1 billion per year.
Phil is right that in structure weight there isn't going to be significant improvement. Though you COULD get significant reduction in payload by using better/efficent rocket fuels (e.g LH&LOX) and lighter electronic and electrical energy generation and storage- solar/fuel cells. And different ways of getting there- crew get to Moon in 3-4 days, and cargo can take weeks or months to get there- and "other things".
With the infrastruture of such a mission mention above you could fairly easily "add" 2 crew to moon and back at a booster cost of around 2 (or less) A5 boosters.
-gb