Seeking Nashville Plumber and Engineer advice

[James Brown]

I am looking for accurate cost to tap sewer lines in Nashville, Tennessee on undeveloped land that is in the city limits? I have researched the Metro Sewer/Water tap fee schedule and read forms on BP that gave an estimate of $9k upwards to $20k.  The property in question will support four to six houses. I am also interested in learning if an Engineer would have to sign off on the process?