I'm a cheapskate, so I procrastinate until I can work on my terms mostly...
The '90 Ranger has the most money in it, but I haven't kept track and haven't had any other mechanics (excluding friends helping me) work on it other than tires and windshields in 20 years... considering the transition the thing has made that isn't too bad.
The most work and money something needed that I got is my '00 Explorer, I got it for $800 with known stripped spider gears in the LS, that fix was free, fixed the next day, drove it around the block (I'm in the country, 7 mile block) and suddenly lost reverse, $900 in parts later (after a year of sitting, and that's friend discount on parts) it's back on the road but I lost the title I had for it ($40 the day I bought it) so had to pay like $80 for a express lost title (out of state of course) then another $200 or so getting plates in Oregon. Then there's drivetrain mods, threw in a 4406 transfer case and Expedition drive shafts at the tune of another couple hundred... then after a year of driving the trans went again and the one thing we didn't replace the first time went out, $200 more for a good used planetary assembly... Of course there's other nickel and dime stuff that I'm not mentioning...
The '97 F350 hasn't been too bad, it does need like $3000 in parts to get to where it needs to be though... injectors, tuner, turbo, high pressure oil pump and the rest of the parts to get an intercooler in it all adds up...
The '97 Ranger is cake in comparison, all included I think I have $1000 in it, and getting 23mpg from 16mpg in the Explorer it'll pay for itself in about 7 months just in fuel I'm pretty sure...