Free tools are not free. You may not pay in dollars but you will pay either in time to deploy and use, or lower quality of results. See for instance this Nature Methods article that looked at about 4,000 papers published in one year and found that of 67% of them used outdated free software that captured only 26% of biological processes and pathways known at that time: PMID: 27575621.
I would recommend iPathwayGuide (www.advaitabio.com). It is not free but it is significantly less costly than IPA.