sorry what mechanics have 20 dollar engine mounts on the shelf for all cars? none that i know of.
There are a few things that may not be right about that quote but gee you should see some that i write at work...
If the mechanic does not know all the little quirks with these cars the quote will always be slightly off, give them some slack they may just be miss-informed. Very easy for forum people who know the cars inside out to pass judgement but this is the internet not the real world of retail.
I suggest getting your own parts such as people have suggested and take said items to whomever you feel comfortable with for fitment. Get pre quoted so there are no hidden costs and you should be ok.
With regards to the fuel tank issue, i would remove the entire thing and have it cleaned out properly with a new pump. If you don't all your new filters and pump will block up with crap that may come loose in the future wrecking your newly purchased parts.
You bought the car cheap and as someone said it needs work, so don't go Jewish on it and you will have a nicely running car.