This process is not the easiest to do honestly, there are a lot of steps that go on with this replacement. I do not have a video or a written blog to assist you in this swap unfortunately. You may want to get a second opinion on the install, $900 may be a tad high. Depending on your skill level you may want to tackle this, but I would check around first off. .
I have a 91 vert that I changed the motor on when I first got it, about 5 years ago. I have to replace it again in the spring, and it's not all that difficult. You just remove the back seat and back, the motor is mounted to the floor behind the back seat and brace. I found it easier to go thru there instead of trying to go thru the trunk, like most books say. 3-4 bolts hold it down and the fitting for the Hyd fluid. I found that it was hard putting fluid in it after it was mounted so you might fill it up before you mount it. Hope that helps.