As far as an extender or access point, it's usually easier to set up if everything is the same brand. I've had good luck with D-Link, but Linksys should be fine, too. If you can run a Cat 5e or 6 wire to a central location and add an A/P, the problem will probably go away.

I started out with nothing & I've still got most of it left
M60 VP160 QS8 EP350
M22 VP100
Algonquins