exchange like yobit or nova charge something like 0.0002btc for withdrawling your coins but some famous exchange like btc-e or bitstamp charges 0.0005 to 0.001btc for withdrawling your coins from there

Some exchanges charges based on %, such as 0.5% up to 2.5% every time you trade. Each exchange is different and please check their FAQ before you make your move.

I want to assure you that there is no where it is cost free just have that at the back of your mind, then you do comparative analysis of whatever each option will be offering and also consider additional cost you might include to transfer it to the spendable currency of yours before you decide to go for any option... My 2 cents...

you have to visit the exchange site that you want to make a trade at and then look for a link about their "terms of services", "FAQ" or some of them have a link at the bottom of the page called "FEES".
then in any of these pages (it is different page in different exchanges) look for the percentage of fees they take on each trade (it is usually 0.2%) and also look for withdrawal fees which is usually the network fee (10K for bitcoin, 1 for Doge,...) also there is a fee for deposits when you deposit "Fiat" only.
i can't think of any other cost than these.

For valid informations, you can read carefully FAQ on there. And if there are not understanding about that, you can send email to their support. I think it will give you clear informations.

Fees are normally around 0.2%. It varies from site to site. Some sites charge you addionatlly for withdrawing funds from their exchange.

Some exchanges also charge different rates in the case you do maker or taker trades:

Maker: You set a buy or sell order and wait for it to be filed.
Taker: You buy or sell at a price someone put an order for.

The makers are the ones maintaining the orderbook and therefore are sometimes rewarded with lower fees. The takers take orders from the order book and therefore sometimes pay higher fees.

Poloniex uses this system recently, so if you have patience, you may want to go there if you want the smallest fees possible.

some exchange applying different prices. but for me the total commission fees were paid very little. was reasonable because they provide all the services on their website.

Yep, I also felt the fee charged to us for transactions in the exchanger is also reasonable. Because we can not exchange money easily without their help. And I think that fees for their operating costs, in order to continue and to improve the quality of their services. Moreover, we will not fall into poverty just because paying a fee. IMO

can't say it was very little if the amount were traded is quite big,just imagine someone trading with big amount of bitcoin like 40BTC at the same time,if the fee is 0.2% (c-cex),it's 0.08 btc at the end,and for some exchangers,picking order will give more fees