Who gets Bitcoin transaction fees?
The fee goes to the miner who mines the block that includes your transaction. The fee is based on the size (in bytes) of the transaction and the age of its inputs (how long ago the coins spent were received).

Transactions get big if they have to "pull in" a lot of outputs from previous transactions and that raises the fee. So if you got a lot of small payments and then try to make a large payment, the transaction will be expensive because it needs to gather all those small payments.