You're going to have to spend money if you want a 500m wireless link.

If a tinker, and no-one local to annoy if your signal gets too good, try adding pigtails to one of the routers and the pringle cantenna antenna. cheap fun and may just work.

In reply to a post by lexion610:

getting internet there is not at all essential, i just like a good project every now and then to get my teeth into as a sideline and the cheaper the better really!

You'll live to regret saying that.

Honestly, I would spend the ££ on a proper link between buildings and have it sorted out in an easy day, rather than spend months fiddling with stuff that fundamentally doesn't have the power output required for the distance.

(Keep in mind that you'll see lots of how-tos using domestic routers, usually from countries where the allowed wireless power is many times higher than the UK.)