FWIW, T-Mobile 2Go will roam automatically or manually on Centennial. You can't do that from an AT&T GoPhone.
Virgin is VERY strong all along the I-65 corridor, from north to south.
Page Plus, Verizon INPulse, and Tracfone on Verizon all have the same basic coverage area, and it is generally pretty good. I have had a LOT of complaints from people I call from a Verizon-based phone about them hearing their own voice echoing. I haven't tried it on INPulse, but it has been true of both Page Plus and Tracfone/Net10 on Verizon. Not sure if it was the phone or the carrier, but it has happened on at least 3 different phone models, so my guess is that it's the carrier.
T-Mobile can be bought (for a minimal user) for $40 per year by buying a $10 card every 90 days. That would only provide 120 minutes (per YEAR), but I was talking about a minimal user there. Once you've spent $100 on T-Mobile, you end up in Gold Rewards status and only have to buy a $10 card every YEAR to keep service active.
Virgin can be had for $5/month with the auto top-up plan at $15 every 90 days. SugarMama bonus minutes can be added to that for up to 75 minutes per month.
Tracfone can be milked in various ways, but the standard retail rack rate would be $20 every 90 days.
Page Plus minimum would be $10 every 120 days.
Centennial Wireless offers its own prepaid plan, but frankly, their prices are ridiculous.
Don't forget 7/11 Speakout Wireless, although you probably wouldn't be able to find a phone in Indiana - I've checked in various locations in Indiana, Illinois, Michigan, and Ohio, but I bought mine in Florida. I could have bought one in downtown Chicago once, but didn't.
US Cellular probably has some Indiana coverage, but not a whole lot.