I never bothered with a dolly before, I pushed, pulled my trailor all over the place with no issues, if its good/strong enough I just let it roll on the trailer jack. (light though, about 3600 LBS).
Make sure you get a good one. I borrowed one from a buddy and bent it first time with my boat. I think if your garage if flat enough you can just roll it on the trailer kick stand wheel.
John, I have a nice manual dolly I bought new a couple of years ago. I'm selling my boat so I don't have any use for it. Your welcome to stop by to pick it up and give it a try. If it works for I'll let ya have it for $20. Shoot me an e-mail if your interested.
John, even the slightest incline makes it a total pain to push or pull the boat using a manual dolly. If you find you can't do it manually I can get you the name of a company that makes killer electric ones. I had to get one last year to get the boat in my new garage and simply love it. Works great, but not cheap like you said before. About 600 bucks.