Giant Magellen and Thirty Meter Telescope are both $billion+ projects.

So, no.

I was only thinking of telescopes that currently exist, since it's hard to determine the cost of something before it's built. Inflation and such tends to make a direct comparison a bit trickier— it's not fair to compare JWST dollars spent in 2000 with dollars that won't be spent until 2025. Plus, even though these sorts of things typically end up being more expensive than the original budget, I'm being optimistic :)