There is no way to answer your question intelligently without more facts.
It's kind of like asking a mechanic how much it will cost to fix your car before he has started the engine or looked under the hood.
You should consult with an attorney in your community who represents landlords in disputes with tenants. Many lawyers offer a free initial consultation, which should include an estimate of the costs involved.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like Avvo, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
Based on the facts this sounds like a 1 day trial. Probably no jury. Attorney will charge for at least 8 hours, not to mention time for preparation.
The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change.
A wrongful eviction case can take anywhere from one day to try to two weeks or more to try, depending on the facts of the case, and depending on whether or not a jury is requested. A jury will be involved if either side requests a jury. Most attorneys charge by the hour to represent you at trial, but not all. What seems clear, though, is that you do need a lawyer. If money's tight, try to find a newly-admitted lawyer who wants to get some trial experience to represent you.
If a judgment has been rendered against you, you can make a motion for reconsideration, or a motion for new trial.
The former requires new facts or law, and must be brought within 10 days, while the latter requires a showing that the judgment is not supported by the evidence.
You also have the right to appeal from an adverse judgment.
If you failed to appear for trial, and did not present evidence that supported your position, it is unlikely you will be able to set aside a judgment.
In terms of the fees that will be incurred in seeking such relief, there is no fair way to estimate without knowing all of the facts.
I would strongly urge you to consult immediately with a litigator skilled in this area of the law.
PLEASE NOTE THAT THIS RESPONSE SHOULD NOT BE CONSTRUED AS A LEGAL OPINION OR ADVISE, AND DOES NOT CREATE AN ATTORNEY-CLIENT RELATIONSHIP. IN ORDER TO RENDER A LEGAL OPINION OR ADVISE, THE RESPONDING ATTORNEY WOULD NEED FAR MORE INFORMATION THAN HAS BEEN PROVIDED, AND WOULD NEED TO BE RETAINED PURSUANT TO A WRITTEN FEE AGREEMENT.