1. Frankly, you're asking for a whole legal education all at once; however:
a) Expungement only follows (or accompanies) a plea of guilty or no contest.
b) Sealing a conviction only happens for some juveniles
c) Sealing an arrest requires a showing of "factual innocence" and can get complicated.
d) No intent to steal involves the defense of "accident" and may require hearings/trial
2. For defending a Petty Theft within a fifteen mile radius, I usually charge $1750.00 for a disposition - and more for a trial. A brief Interview, plea, and request for immediate expungement can be less. I don't know where you are in California.
Ellery Sorkin - 818-995-4367
You've asked a lot of questions. Crazier things have happened, but most likely you will not be able to accomplish all of these goals at the Arraignment.
What you eventually will be able to accomplish depends on various factors including how strong the prosecution's case is and your prior criminal record, if any.
The ideal situation would be charges not even being filed. If charges are filed then next best situation would be the prosecution not having a strong case and it being dismissed all together or going to trial and being acquitted. If charges are not filed or ultimately dismissed you will then be able to seek a finding of factual innocence and have the arrest record destroyed. Regarding a finding of factual innocence - the burden is essentially on you to prove your innocence.
An expungement would only be necessary if you are convicted. If you are convicted and you successfully complete probation you are eligible for an expungemnt. An expungement does not entirely erase criminal convictions from your record though.
Attorney fees really depends on the facts of your individual case. If the case is resolved early in the proceedings fees will obviously be less than if a trial is necessary. Also, an expungement would be an additional cost.
At arraignment, you are simply advised of the charges against you and given an opportunity to enter a plea. The judge will not hear evidence, so there is no opportunity to "defend your case." That's what trials are for.
There is no way to seal a record of an adult conviction in California, and a so-called "expungement" doesn't really clear your criminal record, as some attorneys claim on their websites.
In order to have the arrest records sealed & destroyed, you would have to petition for a finding of factual innocence. Note that this is not simply a dismissal of the case based on insufficient evidence, or a "not guilty" finding because the District Attorney couldn't prove the case beyond a reasonable doubt. You would have to convince the judge you really were innocent -- which can be a very steep burden, except in cases where the DA agrees you were the victim of identity theft.
Under Penal Code §1203.4, a person who is granted probation can apply to have the case dismissed after probation is complete. This is sometimes called an expungement, but it doesn't really expunge anything or seal your record. The conviction is still a part of the court's public records, which will also show the case was dismissed. You still must disclose the conviction when applying to be a police officer or for certain other jobs, or if asked on an application for a state license or to run for public office. The conviction can still be considered a prior offense; for instance, a prior theft conviction could make any future petty theft a felony.
BEWARE of law firms that promise to "clear your record" and charge thousands of dollars. The process of filing a Penal Code §1203.4 petition is pretty simple, and you can do it yourself with forms available from the court clerk's office, especially if you completed probation without any problems. If you had a probation violation along the way, you may want an attorney's help, but the guys who charge thousands to file simple paperwork will probably overcharge you for that, too.
California Labor Code §432.7 says employers can't ask about any arrest that didn't result in a conviction, inquire about it from other sources or use it in a hiring decision.
Some attorneys interpret this Labor Code section to mean you don't have to disclose a conviction that was dismissed under Penal Code §1203.4, but I usually advise clients to disclose it, with an explanation that the conviction was subsequently dismissed.
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 this site, 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.