That is tough. Sites like zillow may help a little but that is only one piece of a larger whole. Without an agent with the experience, training, and tools, to guide you, you will never really know if you are at the right price.
Exposure is important too. It is simple economics. Unless, you can get your home to the masses, you will not be able to get top dollar. More exposure, means more demand, means top dollar. There are transaction brokers who can give you some of that exposure on the MLS and sites like craigslist.com and postlets.com can help with the rest. However, you will need expert help to make sure it looks great everywhere and is everywhere it needs to be.
You will also need guidance with contract negotiation, home inspection issues, monitoring the buyers mortgage process. Those are just a few. Getting your price is one thing, getting successfully to closing is another. Mistakes can cost you thousands. Even though I am a Realtor myself, when I fix and sell homes I still use another Realtor. I find that the third party perspective, expertise, and guidance is priceless. That is not to say it can't be done successfully on one's own, but the statistics are against you. I recommend trying it on your own for a few months first and then find the best agent around if you aren't successful. You'll be glad you did.
Hope that helps.