We know how much new Hubble would cost. The Roman telescope is based on donated donated spy satellite of similar size and design. It will cost estimated $3.2 billion and that doesn't include the mirror and structure.

New Hubble telescope wouldn't solve the Starlink problem. There are lots of smaller ground telescopes that have view blocked. We would need to launch a bunch of smaller, like 1m ones, to compensate. Also, there are a lot of larger telescopes that are only feasible on Earth. Good example is the 8.4m Rubin survey telescope which is only going to cost $700 million but would be lots of billions in space. That might fit in Starship but the Extremely Large Telescope won't.