The problem is that any launch to Mars is going to be really expensive, even if you adopt the cheapest known means (currently owned by SpaceX).

It might be actually cheaper to solve ancillary problems and actually send humans one than say try 20 unmanned missions... With more benefits too.

Or to send more people to the Moon, push the research on in-space manufacturing and bootstrap some semblance of economy in cislunar space. This seems like the most reasonable way to escape the trap of expensive space missions you mention.

The trap goes like this: launches are expensive, so let's get more bang for the buck by putting more stuff in a single mission; this makes mission both more expensive (insurance) and preparations take much longer; this decreases the frequency of launches, which increases their costs.

Getting some production upwell (fuel, vehicle hulls) would decrease cost of launches, allowing for more frequent and simpler missions, and hopefully break us out of this trap.

The payload cost dwarfs the launch cost. These big missions end up "battlestar galactica" (an actual term used) - a big fail would be a disaster so more money must be spent to really ensure success - meaning it's even bigger - meaning risk must be still lowered.

It's a growth spiral leading to stagnation.