For reference, the WFIRST telescope came with satellite bus and 2.4m mirror for free yet already has a 3.2 billion dollar price tag attached to it. Even the most expensive launch provider would be less than 10% of that cost.
It only weighs about 4 metric tons by the way, so there's that.
Just a quick reality check on the unrealistic assumptions some people have.
You might be able to use a commercial satellite bus for example. It would be fine if some would experience failures, as there would be the next one already lined up.
Just put different instrument(s) at the end of the optical path in each. As example, Hubble has five instruments. https://hubblesite.org/mission-and-telescope/instruments
One could start a design from something like CHEOPS with a 30 cm mirror. https://sci.esa.int/web/cheops/-/54032-spacecraft
Maybe more experimental instruments would be nice as well.
The primary cost factors are instrument development, ground segments, staff (over years, e.g. 5-10 years development plus ~5 years primary mission plus extensions), testing, and building (no economy of scale here).
The most counter-intuitive observations is that the cheaper your launch-costs, the higher the portion they represent w.r.t. total mission cost. A "cheap" (e.g. sub-50 million dollar) telescope for example would have launch costs come in at up to 50% of the total cost when launched on a medium-sized launcher or with a second payload.
It's a multivariable optimisation problem and the best solution depends on the variables that you want to optimise for.
A ring of radio telescopes in high orbit would be neat.
https://www.nasa.gov/directorates/spacetech/niac/2020_Phase_...
[0]: https://en.m.wikipedia.org/wiki/Laser_Interferometer_Space_A...
I think people have unreasonable expectations as to what SpaceX can do. I'm sure there are efficiencies to squeeze out of the business, but it's largely from the ops, and infrastructure around the rocket, not the rocket design itself ... design that has not changed significantly in 50 years.
Rockets themselves are as simple as you can get. It's fuel and exhaust and cargo . That's it. Reusability is fraught with issues and no guarantees it's cost effective (maintenance is expensive, reliability suffers, and decreased cargo/revenue due to needing to carry extra fuel for return). But even if reusability pans out, you're not going to get one (or more) orders of magnitude reduction in launch costs from where we are today. You'll get a few percentage points, maybe a few tens of percentage points and that's it.
Reusability is not a panacea. Space Shuttle was reusable but it was not cost-effective and there were no cost savings. Also, reliability suffered and maintenance became prohibitive. In fact, I think the consensus is that the entire program was a mistake.
>Why shouldn't it be possible to do even better than that?
Because reusability has to contend with factors like:
1) Turn around time. How quickly can you refurbish a rocket.
2) Maintenance costs. How expensive is it to recover and refurbish the rocket.
3) How many times can you reuse a rocket.
4) Failure rates. Does reusing a rocket compromise quality.
5) Decreased revenue per launch. Reusable rockets need to carry spare fuel meaning, that your cargo space is cut (and cargo is revenue), and your costs are higher, because you have to still 'pay' to ship that spare fuel along with cargo.
Factors like those may make it that even if there are cost-savings, that those cost savings are not orders of magnitude lower, but maybe something on the order of 10%-50% - which is nice, and you can disrupt the market and make a good business out of it, but it's not anywhere close to the claims that are made. And again, SpaceX has not shown in practice that they can get ANY savings from reusability.
SpaceX has been known to talk bullshit ... or more charitably, they have been known to mix aspirational language into their projections. Case in point, I saw a TED talk with the SpaceX CEO claiming that rocket-based passenger travel is just around the corner and will be faster and more efficient than airplane travel... a claim that on face value is just stupid, bordering on insane.
Most people will remember the achievements and not the bold claims.