Yeah. I had the same problem with gas leaking. After crawling under the car with an inspection mirror and seeing gasoline on top of the tank, I attempted to drop my tank myself. Once I started to lower the tank, I realized that I didn’t have the car high enough to have room for myself and the tank, so I buttoned it up and called a garage. Started the car to drive it to the shop, but now it was leaking too profusely to drive, so I had it towed. Turned out that the leak was a crack in the nylon(?) output fitting at the top of the fuel tank and when I’d started to drop the tank I’d flexed the fitting and made the leak much worse. This fitting is integral to the top of the fuel pump so you can’t just replace the fitting, the entire fuel pump needs to be replaced. (Thanx, Mercedes) The repair came in at just under $800 like your estimate.
After driving around for a few days, I stopped to get gas and just as I noticed the pump hit 9 gallons, I saw gasoline running across the drive from under my car. There is a seal under the lid of the fuel pump; the mechanic hadn’t seated it properly. Of course they did charge me for the re-repair!
If you have the means to get you car up high enough, the job wouldn’t be too hard for the average diy’er but I’d advise having a helper at least to lower the tank. I was working by myself when I tried, and I could only get my car about 13” off the ground! [My smart had about 130K on the odometer at the time]