It is never a good idea to represent yourself when you are charged with a criminal offense. You'll be held to the same standard as if you were a lawyer. You can't count on the judge or the prosecutor helping you to win your case by teaching you what you should be doing.
Eligibility laws differ from one jurisdiction to another, but typically, you have to be at or below poverty level to qualify for a public defender. If you have a job and assets, you're likely to be ineligible.
If you think you can demonstrate to the judge that you can barely make ends meet as it is and that you would face severe financial hardship if you had to retain a lawyer, you can ask him for an indigency hearing. If he grants you one, you would have to be prepared to show your tax statements, pay stubs, bills and expenses to prove you cannot afford counsel. If you win the hearing you get a public defender.
If you lose the hearing, or expect you will lose it, many lawyers take credit cards. That would give you some way to pay your lawyer but to make small, affordable monthly payments to your card carrier.
The overwhelming number of pro-bono criminal lawyers are public defenders. But all lawyers are supposed to do pro bono work now and again to stay in good standing with their bar. You could call criminal lawyers and explain your circumstances and see if anyone will take your case pro bono.
Finally, if there are law schools in your area, many have criminal justice clinics where law students take on real criminal cases for course credit under the supervision of an attorney. These clinics are free or have a sliding fee scale, and when court is called for, the professor goes to court with the student to make sure the case is handled correctly. Many of these clinics have excellent reputations, and that's an option to look into.