Hueydevoted, it has been many years since I let anyone, touch any of my vehicles for service or repairs (all DIY, except a couple of recalls, a broken windshield, and tires), but if I were to take a vehicle in, I would never pre-authorize them to do whatever they thought was needed with the agreement that I'd pay whatever the (undisclosed) total was. You should have been given an estimate up front and then a caveat "but it's possible xyz needs done too, we'll contact you for approval" in cases where that applies.
That is like writing a blank check and some other shops would be far less honest and find (invent) MUCH more wrong. I would always insist that a flat rate charge be disclosed up front and if it is a "problem->exploratory find" type repair, that they contact me once they reach the point of diagnosis, with a repair quote and are only authorized to do the repair upon my approval at that point, then so far I only owe the diagnostic fee... but appreciate that this fee may already reach $100+.
However, you probably knew going in, that you were going to pay a premium for the part, and to be fair to mechanics, sometimes on a (now nearly) 20 year old vehicle, in WI where I assume vehicles rust a fair amount over 2 decades, a fuel filter can be more than a 15 minute job.
Newer vehicle, might be a 5 minute job on a truck where it's exposed right there on the frame rail, but if there is corrosion on the line and the quick release clips don't quick release, it can be an exercise in patience where taking your time instead of brute force (don't want to break a rusty fuel line $$$) is the best way to treat the vehicle properly.
We can't all DIY our repairs, but even if you need a Ford fuel filter clip release tool, it is fairly inexpensive and if you can DIY in 15 minutes, I would, instead of probably far more time and inconvenience than that just driving back and forth to have someone else do it... but back to the issue of maybe it isn't as simple on a truck that old, so if you DIY and your fuel line is toast and then leaks, putting a new fuel line on DIY is a lot more work or having more expense to tow it to a shop to do it.
Frankly once a vehicle gets to that age, I don't feel it is cost effective to keep it if you aren't going to DIY, at least the less complicated things, though in your case maybe there is an exception, considering how much new pickups cost these days!
