Hi, I live in Colombia and I use my iPad with a 3G data plan a lot.
Here we have cellular companies 3 options. Comcel, Movistar and Tigo. All of three have a prepaid data plans. The only issue is that they don't have microsim, I had to cut the Sim card and it works very well on my iPad.
You can check COMCEL, MOVISTAR and TIGO web sites (don't forget to put ".co" at the end) for reviewing all prepaid data plan that they have. You can choose a day, a week and a month data plan unlimited without contract. All of them are 3G.
I hope this information can help you.