Most Dallas defense lawyers offer free consultations. I'm not aware of any taking pro bono cases for actual representation. However, your officer of services in kind may appeal to the right attorney. You should schedule a few consultations, see if you can find the right lawyer to work with your financial situation.
If you end up getting arrested on the warrant, ask for a court appointed lawyer at your first opportunity.
Here is some useful information from the Dallas Public Defender's office. http://www.dallascounty.org/department/pubdefender/adult_criminal_faq.htm
Most lawyers will consult with you for the first time for free. You may be able to get the answers that you need in the consultation, or find a lawyer that will work out a deal as you suggest. If you qualify, you will be able to get a court appointed attorney once you turn yourself in. Remember that it is better to turn yourself in sooner, than to get arrested.