There is no free shuttle from WDW to Universal/IOA. The cheapest way would be to take the Lynx bus, which I really do not know anything about except that it leaves from the TTC and you have to change buses at some point.
The next least expensive way would be Mears Transportation, you call them and make an appt to pick you up at your hotel and then you call them about 2 hours before you want to leave the parks to come and get you. Last year the round trip cost was $12 per person. The last way would be to use a town car service you would need to make an appt with them, the cost is usually $45 to $55 round trip