Average fees are normally between 0 and 3%.
Afaik, if you wanted to mix an altcoin, I think it'd be more likely people would use shapeshift.io to convert it to bitcoin and convert it back at a later time as shapeshift is quite a quick exchange with no sign up options everything's quite anonymous.
There are sutes particularly like chipmixer who round down payments to the closest mbtc and take the extra btc as a donation/tip.
Converting sites like Shapeshift and Changelly allow for mixing through anonymous coins such as Monero as well. The former has teamed up with BCash apparently, make of this what you will.