Cheap bikes are never good... and good bikes are never cheap.. In order to sell the bike at such low prices, they have to compromise on the quality of the parts. Pay a bit more and get a bike with decent parts that would at least last a while.

I have a Cannondale which I bought in 1993, I guess I put in about $2,000 in the bike including upgrades and replacement parts in the 20 years that I owned the bike. That works out to be $100 per year or $8.33 per month. While there may be bikes that are low cost, but they may not last long before the parts start breaking down and you have to spend more money on repairs.