I have done a lot of Mustang upholstery and plenty of headliners, so I though I would try to do my convertible top myself. It turned out OK, but I still have a couple small wrinkles in the sail panel area that I never got out, despite steaming it. Even after reading all the articles and instructions I could get my hands on, it still took me at least 40 hours, and I will never do another. But, I think there is a lot of prep work the average guy can do to save money on a professional install. Typically the front bow area is corroded since it is made of aluminum, so cleaning and prepping this area can save you bucks. Also replacing the tack strips on the front bow as well as the rear bow will save the installer time, and you money. Take out the well liner, clean that area, and replace the well liner yourself after the top is installed. You can also replace the top weatherstrip pieces yourself, as well as making sure the top is lubricated and working well before you bring it into the shop.
A couple other suggestions, don't disturb your top pads, the installer needs them in their original place, they keep the bows at the proper orientation, and unless your top pads are really bad, don't replace them, the originals are much better quality. And that goes for the lower body tack strips as well, unless yours are rotted away, the originals are better. Most top places will sell you tack strip material by the foot, the new stuff is made of urethane, versus the original cardboard type material. Just use stainless steel pop rivets to install it.
GOOD LUCK!
Rick D.