This is great full-body exercise.  It is not uncommon for me to average burning 20-25 calories per minute on a machine like the Concept 2.  That becomes quite a lot of calories over a half-hour or hour span.  You'll never burn them at that rate on an elliptical machine.  A Cybex machine (a cross between an elliptical & a stair-stepper but having variable incline grade & resistance) will come a little closer but it's a rare occasion when I can hit even 21-22 calories per minute on those (again, over an hour's duration).  The rower is also a much more complete upper & lower body exercise.  The muscle groups impacted DO align much better with those you will use while paddling (or at least the ones I use!).

You can "over-do it" on a rower if you are not careful... especially as our bodies deteriorate with age.  I wouldn't do it everyday.  Rather, I've found it works better if it is part of a broader muscle-building and cardio regimen.

There should be LOTS of used ones on the market (e-bay, craig's list, etc.).  Plenty of folks with grand ambitions buy them brand new but they end up gathering dust in their basements or attics.

By the way, anyone interested in "rowing" as a sport or exercise should pick up a book entitled, "The Amateurs" by David Halberstam.  It details the grueling workouts & challenges faced by ambitious, would-be Olympic athletes (a few decades back).  It's a great book if you want to get pumped up about super-conditioning.  What those guys go through is incredible... and inspired me to buy my first rowing machine long, long ago.

Jimbo   8-)