If you're getting a new/used 360, you're better of parting out that console. Sell the board and drive together as a RRoD 360, sell the rol board, the fans, case, etc all separately on eBay to get some money to pay for the new one.
You're best bet is getting a new or used WORKING one that's never had the RRoD.
Doing this, you'll be able to prevent it from getting the RRoD and know that it won't necessarily happen any time soon (RRoD consoles ALWAYS RRoD again).