Doing a primitive martian insert isn't anywhere in the same universe as landing people safely on the Moon or Mars. India will require several decades of further

Doing a primitive martian insert isn't anywhere in the same universe as landing people safely on the Moon or Mars. India will require several decades of further development yet to attempt a human Moon landing (much less Mars). Russia (nor the USSR before it) can't come close to doing it and they're still far more advanced than India in human launch capabilities. There are simple things (relatively speaking) you can slash the cost out of dramatically, where it doesn't translate to a far more advanced and difficult mission, and that includes landing humans on the Moon or Mars safely. NASA can do cheaper missions. There is nothing particularly special about that for such advanced organizations. NASA spends a lot of money because time (getting a mission right the first time) and scarce human resources are both more important to them than sheer dollar cost in most circumstances, unless we're talking enormous sums of money. They could have attempted James Webb in a much faster timeline at a far cheaper cost, by increasing the risk of failure in the mission; that trade-off is almost always undesirable for NASA. Simply put, a few hundred million dollars is a very big deal to ISRO, it's not a big deal to NASA. If spending $1 billion on a mission gets you down to 5% risk, or you can spend $100 million at 30% risk of failure, NASA will almost always choose the $1b option because there are not enough human resources to throw at numerous copycat missions and the time cost is immense.