The gas limit for single send transaction is about 21000 gas which turns out to be 0.000378 ether per 21000 gas, roughly equal to 0.4 US$.
The SafeLow cost for a transaction is currently $0.019, which is a lot less than your $0.40. It's possible, however, that the price has fluctuated since you wrote your question, which I'll talk about more below.
Now I am creating my own Ethereum based crypto-coin, and I want to keep its conversion rate as 1 coin = 1 US$
This is perhaps possible during an ICO phase, where you can sell the tokens for this amount, but how will you prevent them being traded for different amounts on the open market? (This is perhaps worth a new question, if it hasn't been asked before.)
But if my traders send 1 or just half coin, then also for this transaction, if they have to pay the whole gass limit then it will be of no use as it will be more of a loss.
Ethereum's gas prices form a market. As above, I think your estimate of $0.40 is too high, at least for the current market. However, as the number of transactions being sent on the network increases, so does demand for throughput and space in blocks. This pushes up the gas price, and this is how it was designed to work.
Fees will likely be lower when further scalability solutions have been implemented, but the price market will always exist. If that doesn't appeal to you, then perhaps a different platform would be a better fit (and especially if you want to peg your token to a fiat value).