How much does it cost for you guys to convert to fiat,
I don't pay a fee. The fee is paid to me.
I have a valuable thing that other people want (bitcoins). If they want them, I require that they pay me a fee. Then I let them have the bitcoins.
and is the converting process convenient for you?
It is convenient for me, but it probably helps that I'm not in a hurry to convert.
I simply put a listing on localbitcoins.com and then wait for someone nearby to want some bitcoins. They pay me for the bitcoins PLUS the fee that I set when I created the localbitcoins advertisement, and I send them the bitcoins.