There will probably be no warrant issued, until after you fail to do as you were instructed per the DA's letter. Did the letter give you a date to appear in court to show proof of enrollment or completion of the class?
Basically, if you ignore this letter like you ignored the problem you caused with Wal Mart, then this will snowball into a bigger problem, just like it did with Wal Mart.
If you have a court date and do not show up, the judge will issue a bench warrant. If you have no court date and decide to ignore the DA's letter, it can result in an arrest warrant being issued.
Either way, the least the judge will do is require you to take the class your claiming you can't afford to take. However, the judge can add an additional fine, penalties, court costs, etc. So this situation will only grow more expensive and require more of your time if you choose to ignore it. You should know this by now, unless you have not learned anything from what has already grown after planting your seven dollar seed of stupidity.