Contact the Florida Department of Revenue, Child Support Enforcement Division and enroll in Title IV-D child support services. If you are receiving any form of Public Assistance (e.g. TANF, AFDC, Food Stamps, Medicaid, welfare, etc), then you will be a PA client & your rights are already subrogated to the state pursuant to F.S. 409 anyway and they likely will be (if they have not already) contacting you to start the support cases. If you're not receiving any public assistance, then you can still enroll - you'll just need to fill out some paperwork (equivalent to giving them a Power of Attorney) so they can proceed on your behalf - and then you'll need to cooperate with the process.
The answer provided is a general answer to a general question - and should NOT be construed as my giving specific legal advice, nor does it create any attorney/client relationship or expectation of privilege - and should you have specific questions you seek to address, then I encourage you to seek a consultation with an experienced Family Law Attorney in your area who may discuss your case with you and give you specific advice to assist you.
If you don't want to spend any money, you'll have to go through DOR. It will take longer, but it's free. Prepare yourself because you will likely end up in court at some point.
Legal disclaimer: Ms. Braaten's answer to your question does not establish an attorney client relationship, but rather is meant to share knowledge with the general public. For specific advise on your case, you need to consult one on one with an family law attorney.