Concept2 is basically the de facto standard for rowing machines, anything else isn't really worth it in my opinion. Stay a member at the gym. 3x week weights, 3x week 7500m erg (i.e. on the rowing machine). Alternatively if there is one nearby you can look into joining a rowing club. These almost always have ergs you can use, and some even have weights. This being on top of the opportunity to actually row for real, which I can assure you is much more entertaining than erging!