welcome to the site!
1. I don't know cost as I do as much work as I can on all our vehicles. I don't have a manual handy so I don't know the 90k, if it exists?, but I know at 105k it is highly recommended to replace the timing belt and associated gears/pulleys. There are quite a few other things I'll do when I replace a timing belt, like replacing the water pump, front and rear crank seals, cam seals.. there are a few other things I saw on a list a couple days ago as well. The main reason I mentioned these things is for you to look at what all is included on the labor for the 605-725 bills. If you think it will help, you can mention a quick breakdown for each quote. The guru's here I'm sure will point you in the right direction.
2. the plastic shroud under the front of the forester will catch quite a bit before it spills over. Consequently, while you drive, it dries out a bit, flies off, etc and you won't see the results of something going bad for a while or too late. If you throw down a blanket or piece of cardboard and open up a few of the access holes you can look for yourself with a flashlight. Look for staining on the exhaust heatshields, gummed up caked on oil/dirt mix at the bottoms of where the cylinder heads meet the engine. (Unrelated to a HG, you might also check the oil filter/cooler for dripping, the water pipe that goes to the oil cooler for rusting.)
not perfect answers for you but certainly trying to be helpful.
edit>> I must have opened the screen just before you posted. well put :)
04 XS leather
03 XS leather
91 Ford Festiva