Concept 2 ergometers, model D, are the gold standard. Used ones can be found for around $600 to $700 and new ones are $950. Many gyms sell their rowing machines because people don't use them, however, crossfit studios snap them up. Check your local craigslist. There's also RP3's from Row Perfect, but they're $3,500. Some swear by the RP3's as feeling much closer to rowing on water.
