I count 13 on wikipedia's list of the largest telescopes. There are 3 more currently under construction. The evocatively named "Extremely Large Telescope" is estimated to cost about $1 billion USD. Who knows how much it will actually cost, but for comparison, that's about $400 million less (adjusted for inflation) than the budgeted cost of the Webb telescope, which is about 1/6 the planned size (and therefore 1/36 the light collecting capability).

edit: italicized above. The Webb ended up costing $10 billion, so the savings could be even larger