The main bunch of fun is going to be dropping the tank, removing/installing the sending unit without igniting the fumes (use a non-metallic object or brass hammer/punch to knock off the retainer ring), and then wrestling that bugger back up into place. An extra set of hands makes it MUCH easier. I wouldn't pay someone $400+ to mess with it. Buy the part new (don't bother with a used one, you don't want to have to re-do the job if it goes bad), and hire a buddy to help you install it. Might take you about 3 to 4 hours, tops.
Basically, all that's involved is: backing the car up on some ramps, loosening the fuel filler neck from the filler door, unbolting the tank holding straps, knocking off the retainer ring (hammer and wood block worked for me before on my previous 'Stang), removing the old unit and putting in the new one, knocking the ring back into position, and then the REALLY fun part ... lifting that turd back up into position and holding it there while you try to get those holding straps back into place, AND getting it lined back up with the filler neck. Again, an extra set of hands makes it MUCH easier, but theoretically you could use a jack and get 'er done ... it's just a major PITA that way.
I've had a brand new sending unit sitting in my closet for about a year now (about $90 from 50resto.com), and I can't ever get around to it because A. My stupid HOA won't let me work on my car in my driveway anymore, and B. I can't convince anyone to volunteer a couple hours of their time to help me lower/lift the friggin' tank.
Until then, just use your trip odometer to figure how much gas you've got left. I refuel when I get close to 150 miles (which is about 1/3 tank left for me), then reset it when I fill up. You could probably go as high as 200 miles, but unless you really know how much gas you've got left, you're kinda taking a gamble on running out of fuel at that point, depending on what kinda mileage you've been getting for that tankful. Been driving the car this way as long as I've had it, and I have to do the same thing with my Lincoln Town Car because the stupid sending unit in that thing only works half of the time (stupid digital dash readout gauge).
