Check out great discount rates from Hotel Engine!
If you're looking to stay close to the park for the lowest price, you will want to aim to be south of or right on 465 South (see map below).
Indy's southside is generally a good area, so you'll find plenty of 3 and 4-star accommodations on I-69, 465, and off of Meridian St/31. Everything in this region is basically 20 minutes or less from the park!
Using Hotel Engine, you can search this area specifically or look for terms "Southport", "Greenwood", "Homecroft" to narrow down in some of the common suburbs.