Have you looked at pandoc?
It’s a command line tool, but pretty simple and there is a lot of help on the net about it. Handles bibliography as well. The basic command is pandoc input.md -f markdown -t latex --natbib -o output.tex or similar.
(I have not tried to export multiple files at once and don’t know if it’s possible – my first attempt would be to first concatenate them and then export the resulting .md.)
But if you don’t use any markdown syntax, can’t you just copy-paste it?