Indra lok is same as Swarg lok as Indra is considered the king of Swa lok or Swarga lok (heaven). As per Vishnu Puran, the distance between bhulok (earth) and swalok (heaven) would be 1 lakh yojana (8 lakh km).
It states, surya mandala (the zone of the sun) is situated 1 lakh yojana away from earth.
bhūmeryojanalakṣe tu sauraṃ maitreya manḍalam [VP - 2.7.5]
And, from surya mandala onward the 14 niyuta yojana (approx. 1120 lakh km) till the Dhruva star is known as Swa loka:
dhruvasuryāntaraṃ yadya niyutāni caturdaśa
svarlokaḥ so'pi gadito lokasaṃsthānacintakaiḥ [VP - 2.7.18]
Those who analyze the position of different zones state the fourteen niyuta yojana between the sun and Dhruva as Swa loka.
So as per the scripture, basically after 8 lakh km from earth the region of swarga would begin.