There's something I don't understand about the bid vs ask price spread on fx markets:

For example, assume the lowest ask price is 200, and the highest bid price is 100. So if I want to buy now I need to pay 200, if I want to sell now I will get only 100. 

In this situation can't I place a bid order for 101 and it will be the best offer so I will buy shares for this price? And can't I place an ask order for 199. Again, it will be best offer so I will sell shares for this price.

Summarizing, I showed I how to buy for 101 and sell for 199. In this situation spread is my profit, not cost. Where I am wrong?