When I did my first room (study) I rented a manual nailer for $25/day. I used it for three days, so it was $75 and my arm felt like a wet noodle when I was done. So, since I still had several rooms to go, I decided to buy the Harbor Freight air-powered nailer (you need a decent air-compressor). I knew I would spend more than the cost of an air-powered gun on rental costs, so I decided to buy it. I bought it on sale for $99 so it was a no-brainer for me. Even at $169 I'd still buy it if I had it to do over. I've used it for a large living room, a hallway, and a back bedroom and so far it has help up well and done a great job. Once I get the Master bedroom done I'll probably sell it on Craig's list.
Unless you're planning to do flooring for a living, the HF mailer is just fine.