If you search "RMVB" on Ebay you will find many of the RK2706 players I could also recommend them as they're the newest so include more features and can play more video files
(Why RMVB, well because these new RK2706 are the only ones that support RMVB earlier versions didn't and as RMVB is a format only commonly used by chinese you won't find much other products then the players)
Have a look here -->
Mpx players with 'rmvb' on eBay.