My current (rental) place has the router and AP in one corner of the apartment, so signal strength at the other end is terrible. Is there a better (cheap but effective) option than this?
As with the original link, the antenna is directional (and since it's a reflector, probably even more directional), so you lose out on flexibility. It'll be quite good if you don't plan on moving the other point, though.
Better is to get a WDS bridge (wireless repeater). A high gain antenna (higher than in article) won't work well in the "long house" scenario because two clients may not be able to hear each other and may thus collide. (RTS/CTS is supposed to fix this but it relies on clients choosing to use it.) Unfortunately with WDS, the bridge must be the same brand as the AP (which itself must support WDS), so you might be stuck purchasing two new pieces of hardware.
But if the clients are all near each other, you have some money to spend (~$100), and don't mind being stuck with one band (2.4 GHz or 5 GHz), I'd recommend one of these:
As with the original link, the antenna is directional (and since it's a reflector, probably even more directional), so you lose out on flexibility. It'll be quite good if you don't plan on moving the other point, though.