The Tenda N301 is a cheap but functional 2.4 Ghz wifi router. It will not run OpenWRT nor DDWRT and is a single band router. I buy them at Microcenter sometimes on sale for less than $10. The documentation at http://www.microcenter.com/tech_center/article/3006/HOW_TO_Set_Up_a_Tenda_Router_as_a_Repeater is obsolete. The current documentation is at http://www.tendacn.com/en/faq/2808.html
You need to have two N301 routers and both powered on. You may have to switch from R1 to R2 and vice versa during configuration. You will know you are done when you can ping R1 from R2.
If you run into trouble, you may need to reset one or both routers and try again. If 7 seconds on the reset switch doesn’t work you may need a hard reset - http://compnetworking.about.com/b/2009/03/11/the-30-30-30-hard-reset-rule-for-routers.htm - note you will be holding the reset button in for the entire procedure.