The thing is, RRoD 360's are generally a dying breed. My first Xbox 360 had it and had it 3 times to be exact. The first two times, Microsoft decided to "fix" it for me for free. Although, each time they sent it back to me, they sent it back in the same condition. I just sent it away again and it seemed to fix itself. That was fair enough and a long time ago. I now work with these consoles and after I talked to Microsoft regarding our policy for taking back RRoD consoles, I was informed that the RRoD is now pretty much eradicated. They found that the Xbox Pro package was at fault and some component was causing it to happen. Since they don't make the Pro consoles any more, it has all but disappeared. It will still happen from time to time but that is on rare occasions. Microsoft informed us that if it does happen, we have to return in to them immediately as they are trying to get rid of the problem forever.
Buying an RRoD 360 could be good or bad. There is a few very cheap ways that you can fix an RRoD 360 and I have done it myself. It is simple and will cost you 8 pence. However, it could be trashed and beyond repair. I think you ought to find out exactly why it is RRoD and then I could perhaps give you some tips on fixing it. I think you should probably just get a new arcade though. It is not that much more expensive and you will have a two year warranty on it automatically.