There's one BIG problem with having a paralegal or 'preparer' do your forms - they CANNOT PRACTICE LAW ! They cannot advise you on the law (illegal practice of law), and they cannot help you in court if anything goes haywire. They also do NOT know anything about the habits and character of the Trustees in your area, and a lawyer that knows what a Trustee will look for, will pick on, or even what their mood is generally like is quite valuable.
Filing yourself CAN be done but even the simplest of cases can go wrong with one mistake. Many people DO file w/o a lawyer or a paralegal and they do so successfully, but you CANNOT go into this kind of thing thinking its a cake-walk - its FAR from it. You need to READ, READ, READ, do your research, read the BK code too. Do you know what expenses and at what levels are acceptable in your area ? No, but a lawyer does. A good bankruptcy lawyer can take one look at your budget and tell you what will and will not pass muster with a Trustee.
You CAN pay the filing fee in installments. You CAN pay the lawyer's fee in installments, but most won't file until you're paid in full. There ARE lawyers who will do BK cases pro bono, and you MAY qualify for legal aid to help you.
I know quite a bit about bankruptcy and the process, but there's no way I'd file bankruptcy w/o a lawyer !