i'm in the same boat (except it's been six months longer - left in july!). i'm planning to use my tax refund for my court fees. not using a lawyer, neither is stbx. i figured out the process by going to my county courthouse website and downloading all the forms. online resources like that obviously vary widely, but if you go into the courthouse, they should have all the forms with instructions that walk you through the process.
in my state, there are two ways to start the legal process:
i can fill out the petition, have stbx served, and file the petition along with the affadavit of service ($400 + whatever i have to pay the server). then he would have 45 days or something to file his "answer" (costs him $400). if he files that answer and we disagree on a bunch of stuff, we would get ordered to mediation ($1500-$2000).
we can fill out a joint petition, where we have already reached our own agreements (not sure if this is $400 or $800).
so. he wants to file jointly, and i'm pretty motivated to do that because it could save a lot of money, compared to me serving him, and him filing an answer, and going to mediation. however, there is a very real possibility that i could serve him and file, and he would not get around to filing his answer, and not show up to court, and i would get a judgment without his input at all. obviously that's appealing. however i think i will try to sit down with him and work out a petition that we can file jointly. if we can't do that, then i will just have him served and let the chips fall where they may.