Can't afford a rowing machine?

Here's a cheaper alternative.

First, get these or something like it.  It needs to have the door anchor that you put in the door jamb.  Once you get the resistance band set up in your door jamb, you're ready to row.

Next you're going to put on a YouTube video.  You'll only need the audio, so you can set this up in another room so long as the speakers are powerful enough for you to hear it clearly where you'll be doing the rowing.  This is the video you want:

In the movie, the galley slaves row on a four-beat cycle.  We're going to go at twice that rate.  We're going to heave on one beat and ho on the next one.  Keep in time with the hortator's drumbeats.

You should be feeling the strain by the time you get to the "ramming speed" part.  By the time the hortator says "rest," your arms will want to die.

So there you go.  Enjoy your rowing workout.  :D