I have a base price I tell clients I simply start at.  Yet, I ALWAYS quote the search.  Meaning I pull it back the (say) 100 years, and decide what I want to charge from there.  I know some people say to charge by the hour, but I've found that to be an issue around here.  Basically if you have the chain, and you have done title work long enough - you should be able to gauge how long it will take you, and what you want to charge!  When in doubt to charge more or less, just charge more LOL!  Sometimes we don't give ourselves enough credit :)   Also if I run into ANY issues where I feel I need to charge more (from the original quote) I will immediately contact the client and let them know.  

Finally, I don't take on any projects that I find are too overwhelming, or time consuming.  I like a large good paying project, but when someone is wanting 30 commercial lots done in a month - I don't think so!  I even turned one down recently I had done before - but they wanted me to go waaaaaaaaaay back from what I had already - and I knew it was a mess.  NO THANK YOU!  So just trust your gut instinct, have some base rules for yourself to go by, and you should be golden!