Whoa there nelly, hold on a second.  The reason one gets stale/reject shares may have nothing or everything to do with you.  Here some questions to ask before you jump.

1. How many and how often are you getting stale shares?  Is 1 or 2 every few minutes/hours/days/weeks?  Occasionally get a run of stale/reject is normal, the internet is just like getting stuck in traffic sometimes.  Something happens and traffic slows down. 
2. If I change mining pools do those numbers change?  Do they increase or decrease?  If they decrease, then it probably on the mining pool side, skip the getting the router.
3. Do I see issues with other internet connected devices (TV/gaming consoles/web browsing, etc)?   If so, contact your ISP/Service provider you may have a wire issue. 
4. Is my mining connection via WiFi.  Well that alone is probably a issue unto itself.  But in our daily lives WiFi congestion is a fact of life and can cause latency thus stale/rejected shares.

This is just a few things that come to mind.  So before you go spending your hard earned money, make sure that its addressing a valid issue.