Hi Sushant,
This topic has come up a number of times in this forum, and here's the most common feeling here:
Don't limit your choices by using only cost as a factor, particularly with the 'starting fresh, so don't want to buy a costly bike' constraint. Buying a cheap bike might well translate to poor experience which might put you off biking altogether. Moreover, if you get more serious about biking, you'll realize that what you have is a piece of junk with zero resale value. If you buy a decent bike to begin with, you'll get a far better quality of experience and even if you should want to sell it off, you'll get a good resale value;
I don't know too much about these bikes you've indicated, but they are commonly known as BSOs; bicycle shaped objects, with super cheap and unreliable components. It'll be a pain to ride them and you'll have recurring issues with breakdowns and repairs. Gears, shifters and shock absorbers etc will be the most unreliable components in these bikes. Choose what you want after doing your homework. Here's a small starter's checklist I put together:
/Prashanth