How much is a flight from Baltimore to Indianapolis?

Looks like spirit is going to be the cheapest

You usually get the best travel rates from the airline directly from their website. Try Southwest or Delta.

I've been paying 29 bucks to fly from Baltimore to denver every 10 days

Google flights search provides a good comparison of most carriers and indicates whether southwest has a route there. Of course, you have to check Southwest prices separately.

Try cheap o air

Varies depending on the airline. You should research the different airline prices.

You should put that into the Google search bar and find out that way. Prices vary for different airlines and different times of day. For instance a red eye flight on a Wednesday could be very cheap, but a Monday morning flight would be expensive.