There is no charge for locking a mortgage rate. The first step in looking for a lender is how is their reputation in the marketplace. The mortgage market has been shaky the last couple of months and working with a reputable lender is key in getting treated fairly and honestly. Don’t get charged more than you have to. I am a Mortgage Banker with a very reputable lender, one of the biggest in the USA. A lender should be able to give you a GFE once they have gathered all your info and they should know if your loan can be approved or denied.
Yes this is typical of lenders to charge a “lock” fee particularly now when loans are getting tougher to do. Just be careful of the timeframe that the lock is good for because if the time goes by they can charge another lock fee to re-lock.
I don’t know what you are saying about lock fee vs. a good faith estimate. It is law, in California, that the lender must give you a good failth estimate within 3 days of taking your 1003 application. If they don’t they are in violation of the RESPA law.
If you are working with a reputable lender company than you should feel safe. If it is an unknown or a broker then be more careful and check there references.