Misdemenor theft in Illinois, how can I get Diversion?

You would certainly seem like a good candidate for some form of alternative sentencing.  You could try and represent yourself and hope that the DA's office will work with you, however, that's risky. Your chances of getting the penalties minimized are much greater with legal representation.  You can try legal aid or see if there is a law school nearby, they run free/low cost legal clinics.  Otherwise you need to hire a lawyer.

Possibly they will be able to get the charges thrown out on a technicality or at least reduced.  You need a professional to help; you of all people should get that.

Frankly, you have alot at stake here.  Whether you have to beg, borrow - not steal - get an attorney.  It may seem like a lot of money now but down the line it will be an investment that will pay for itself.  Not having a criminal record will be invaluable, particularly for licensing purposes.

Note:  Even with diversion there will still be a record of your arrest.  You will need to move for an "expungemnt" ( ie clearing of your record).  However you would have to wait the statutory period of time for this.  In Illinois, typically it's 5 years but as little as 2 for some misdemeanors.