Steve,
I don't include rails or spindles in my price. I just charge a flat rate for s.f. of floor boards, which actually includes the cost of doing the rails and spindles. My AVERAGE rate is $2.50 s.f. This covers the cost of spraying spindles/railings. I agree with Deckworks about spraying these. It goes WAY faster. I have not used the clamp/drop cloth method yet, though. I have my helper stand opposite of me with a sheet of cardboard (you can cruise through Sam's Club or Costco and walk out with about 50 sheets of FREE cardboard).
I thought about breaking up my quote to include a rate for floor baords (s.f) and a rate for railings/spindles (l.f.) and a rate or lattice(l.f.) but decided it was too cumbersome and confusing for the customer. I make it a point to explain that my s.f. rate is higher than most, but that is why...it includes the rest of the deck. They seem to like the simple math as opposed to the "fuzzy math".
As for coverage...I use Ready Seal exclusively. I do get an average of 125 s.f. The key word here, is "average". I've gotten 150 s.f. and I've gotten less than 100 s.f. It depends on how thirsty that wood is. Watch the floor boards by pools and boards that get beat up by the sun really SOAK up the sealer!!! It's like watching your dollar bills fall between the floorboards and you can't get them back