We outsource as well have an in house sound post....This is just an advice :
To get a proper quote from anybody serious you must provide the following information:
1) How many minutes ( hours) of raw material you have to get to the 20 min final result.
2) Is it scripted, slated or are there any information about the raw footage or does the editor have to browse thru it all and log it himself.
3) Does the material require sound work ( ie clean up the existing sound add a library sound effects etc..)
4) Does the material require any color corrections?
5) will there be any effects ( incl. any credits)
6) will it require sound mix and mastering and to what format.
Without this info you are just "shooting the breeze"
On the other hand, if you list all of it here, I will suggest what the costs may be from a real editor
