My first thought would be to buy a good antenna for the primary router.
Next would be to buy a stronger primary router in the first place. Perhaps convert to wireless n from g if that is the situation.
If distance is a problem, I see no solution to connecting a remote wireless router except with a cable. Otherwise, you will have the same distance issue as now. A long lan cable is not expensive; I ran one from the upstairs router, outside the house, and back in downstairs.