Dawg has a great idea. You're right when you say that making power from an HD is a spendy proposition - it sure as hell is, but it's possible to leave your motor basically stock internally, add a tuner, exhaust, and air cleaner for under $1000 and easily gain the 10 hp. you originally inquired about. Even if you go with a cam and tuner like Dawg suggested you'll likely end up with these additions anyway. True, it'll never be a tire burner but either way the smile factor will go way up.

 

What air cleaner is on there? If it's stock, there'e a place to start. Any of them K&N, Screamin Eagle, Ness Big Sucker, are gonna give you a little gain. Actually, for the $, a lot they're not expensive. What exhaust is it? Might get a little help from a 2 into 1 also, Rinehart maybe? I like Rinehart but there are a lot of others out there. Step 3 would be a cam, I have an SE 203 in my 88 and it helps a good deal, mostly at the higher RPM's though. None of these things are miracle cures, but the wife and I never have a hard time passing cars or keeping up with the pack, even the guys with the 95 kits. Oh sure, if we drag raced I'm sure they'd win, but we keep up all day when riding on A sunday.

 

Vance & Hines Fuelpac, airfilter and hookerpipes work for me. I can run with the best
and run for thousands less. Fuelpak sells and make a lot of riders happy for less.

 

I too own a "04" Ultra. I serviced this bike for the former owner from the time he bought it new. It was a DOG! Gas mileage was unbelievable upper 40's most the time. After I bought it I made one trip with it and tore in to it as soon as I got home. I would recomend this. Cams and Power Commander. I used HD 203's and very happy with results. Passing is not a problem and still getting 40 MPG. I did this thinking if I needed to go further I could and this would need to be done anyway. Hope this helps. Good luck.