Windshields and back windows go in with a kind of "rope caulk" as an adjustible seat for the glass. Then it essentially is caulked in (around the edges) with a black or charcoal silicone. The chrome surround is held in by spring clips seated on small steel studs that sick out of the body well (around each window). If those stus are broken or rusted off, it gets complicated in a hurry. Glass installation kits can be purchased at most any automotive shop. It is way easier to put new glass in than it is to take old glass out. It is a two man job though because you need to have hands inside the car and outside the car to set the glass in the proper location. If you stick the glass in the wrong spot, it can be kind of hard to move it.

If you have rust trough at the window sills, it really needs to be fixed before putting the glass back in or it will just keep coming out. Bondo is not a good solution here. New metal is well worth it.

Talk to Joe (68firebird400) he did his own vinly top installation. But $750 is somewhere between high and OK. (if they supply the parts, I'd say the $750 is good.)

I'd shop the metal repair around a bit. That seems high to me. I think the vinyl top and glue could be $200 for materials alone. If you mess up setting the vinyl on the glue, you don't get much of a chance to move that around either. You have to be a bit of a perfectionist to get vinyl tops looking ggod. I'd ask the $150 guy to show you some of his past work, cuz it can look bad in a hurry.