You can get a warranty with a used bike for a reasonable price. A new seat is about 400 bucks for a soft tail, dyna etc. A gel seat is good for your passenger if ya have one.
Before you decide to buy a new bike get a harley catalogue and take a look at what you might want to get "incrementally". They should just give you the bike for free and hand you a catalogue. I have about 15k in "incremental" stuff on my Road King and still want some more, just haven't had the time to gete the stuff. So there is probably another 3 or 4 k that will be on the bike before summer comes.
There are a lot of great bikes that have few miles on them cause the RUB's bought it tricked it out and rode it to the local Harley hang out and got way skerred then rode it back to their garage which is where it stayed. Mine is an '05 had less than 2000 miles on it when BM bought it for my birthday last March 18th one year today. Been ridden 22k miles and has been no problem.