Pro se means representing yourself. The forms won't cost anything, but you'll pay filing fees and possibly service fees (to have your W served with the lawsuit). The fees will vary based on your jurisdiction.
If you and your W agree on all the issues, it doesn't have to involve attorneys (though you might want to talk to one, as OwnIt notes, to make sure you're doing everything right and that your interests are protected).
If you want to skip a trip to the clerk/court house, try googling "pro se divorce <your state name>" or "divorce without lawyers <your state name>" and you'll probably be able to find court approved forms for use in your state. Avoid clicking on a site that looks like a law firm, it should mostly likely end in .gov or .<state>.us
The forms may stipulate the terms under which they can be used (i.e. "divorce without children or significant assets")
